Bicycling is good exercise; ________, it does not pollute the air.

A、<span lang="EN-US" style="font-size:12.0pt;font-family: &quot;Times New Roman&quot;,serif;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">nevertheless</span>

B、<span lang="EN-US" style="font-size:12.0pt;font-family: &quot;Times New Roman&quot;,serif;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">besides&nbsp;</span>

C、<span lang="EN-US" style="font-size:12.0pt;font-family: &quot;Times New Roman&quot;,serif;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">otherwise</span>

D、<span lang="EN-US" style="font-size:12.0pt;font-family: &quot;Times New Roman&quot;,serif;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">therefore</span>