取消上一次命令的操作是（ ）

A、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " times="" new="" roman";="" mso-hansi-font-family:="" "times="" mso-font-kerning:="" 1.0pt;="" mso-bidi-font-family:="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">输入字符</span><span lang="EN-US" style="FONT-FAMILY: " times="" new="" roman","serif";="" font-size:="" 10.5pt;="" mso-bidi-font-size:="" 12.0pt;="" mso-fareast-font-family:="" 宋体;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">U</span>

B、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按空格键</span><span style="FONT-FAMILY: " times="" new="" roman","serif";="" font-size:="" 10.5pt;="" mso-bidi-font-size:="" 12.0pt;="" mso-fareast-font-family:="" 宋体;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"=""></span>

C、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按回车键</span>

D、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按下</span><span lang="EN-US" style="FONT-FAMILY: " times="" new="" roman","serif";="" font-size:="" 10.5pt;="" mso-fareast-font-family:="" 宋体;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">Esc</span><span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-font-kerning: 1.0pt; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">键</span>

B、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: \'Times New Roman\'; mso-hansi-font-family: \'Times New Roman\'; mso-font-kerning: 1.0pt; mso-bidi-font-family: \'Times New Roman\'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按空格键</span><span style="FONT-FAMILY: " times="" new="" roman","serif";="" font-size:="" 10.5pt;="" mso-bidi-font-size:="" 12.0pt;="" mso-fareast-font-family:="" 宋体;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"=""></span>

C、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: \'Times New Roman\'; mso-hansi-font-family: \'Times New Roman\'; mso-font-kerning: 1.0pt; mso-bidi-font-family: \'Times New Roman\'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按回车键</span>

D、<span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: \'Times New Roman\'; mso-hansi-font-family: \'Times New Roman\'; mso-font-kerning: 1.0pt; mso-bidi-font-family: \'Times New Roman\'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">按下</span><span lang="EN-US" style="FONT-FAMILY: " times="" new="" roman","serif";="" font-size:="" 10.5pt;="" mso-fareast-font-family:="" 宋体;="" mso-font-kerning:="" 1.0pt;="" mso-ansi-language:="" en-us;="" mso-fareast-language:="" zh-cn;="" mso-bidi-language:="" ar-sa"="">Esc</span><span style="FONT-FAMILY: 宋体; FONT-SIZE: 10.5pt; mso-ascii-font-family: \'Times New Roman\'; mso-hansi-font-family: \'Times New Roman\'; mso-font-kerning: 1.0pt; mso-bidi-font-family: \'Times New Roman\'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA">键</span>