图示四种截面的面积相同，则扭转剪应力最小的是( )。

• A.<img src="https://timg.fentiku.com/97/2016/12/22/jj9PqikZqq.png" title='jj9PqikZqq.png' alt='jj9PqikZqq.png'/>
• B.<img src="https://timg.fentiku.com/97/2016/12/22/loq3sFQD4J.png" title='loq3sFQD4J.png' alt='loq3sFQD4J.png'/>
• C.<img src="https://timg.fentiku.com/97/2016/12/22/KcRkvVPuOM.png" title='KcRkvVPuOM.png' alt='KcRkvVPuOM.png'/>
• D.<img src="https://timg.fentiku.com/97/2016/12/22/RAMVwGgAwa.png" title='RAMVwGgAwa.png' alt='RAMVwGgAwa.png'/>

正确答案：A