刚架受垂直荷载如图示，下列四种弯矩图中( )是正确的。

• A.<img src="https://timg.fentiku.com/97/2016/12/22/adSXGxINNS.png" title='adSXGxINNS.png' alt='adSXGxINNS.png'/>
• B.<img src="https://timg.fentiku.com/97/2016/12/22/6siJUTxNS8.png" title='6siJUTxNS8.png' alt='6siJUTxNS8.png'/>
• C.<img src="https://timg.fentiku.com/97/2016/12/22/r29IV53dff.png" title='r29IV53dff.png' alt='r29IV53dff.png'/>
• D.<img src="https://timg.fentiku.com/97/2016/12/22/r8U1OuSDVR.png" title='r8U1OuSDVR.png' alt='r8U1OuSDVR.png'/>

正确答案：A