在设计楼梯时，踏步宽 b 和踏步高 h 的关系式为（    ）

A、<span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">2h</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">＋</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">b=600</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">～</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">620 mm</span>

B、<span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">2h</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">＋</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">b= <chmetcnv w:st="on" tcsc="0" numbertype="1" negative="False" hasspace="True" sourcevalue="450" unitname="mm"> 450 mm </chmetcnv></span>

C、<span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">h</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">＋</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">b=600</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">～</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">620 mm</span>

D、<span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">2h</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">＋</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">b=500</span><span style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-bidi-font-family:="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">～</span><span lang="EN-US" style="FONT-SIZE: 10.5pt; FONT-FAMILY: " times="" new="" roman";="" mso-bidi-font-size:="" 10.0pt;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa;="" mso-fareast-font-family:="" 宋体"="">600 mm</span>