图示结构各杆温度均匀降低△t，引起杆件轴向拉力最大的是：

• A.<img src="https://timg.fentiku.com/97/2016/12/22/u2vrIIEb3b.png" title='u2vrIIEb3b.png' alt='u2vrIIEb3b.png'/>
• B.<img src="https://timg.fentiku.com/97/2016/12/22/g59uQoufrb.png" title='g59uQoufrb.png' alt='g59uQoufrb.png'/>
• C.<img src="https://timg.fentiku.com/97/2016/12/22/YzcW6ntbNf.png" title='YzcW6ntbNf.png' alt='YzcW6ntbNf.png'/>
• D.<img src="https://timg.fentiku.com/97/2016/12/22/y8a3vBFSxP.png" title='y8a3vBFSxP.png' alt='y8a3vBFSxP.png'/>

正确答案：B