图示结构，C点的竖向变形为f转角为θ，则A点的竖向变形f应为下列何值？

• A.f<img src="https://timg.fentiku.com/97/2016/12/22/p42LyThgwR.png" title='p42LyThgwR.png' alt='p42LyThgwR.png'/>=0
• B.f<img src="https://timg.fentiku.com/97/2016/12/22/mSvsQWcEiC.png" title='mSvsQWcEiC.png' alt='mSvsQWcEiC.png'/>=f<img src="https://timg.fentiku.com/97/2016/12/22/dYtKrfWZv5.png" title='dYtKrfWZv5.png' alt='dYtKrfWZv5.png'/>
• C.<img src="https://timg.fentiku.com/97/2016/12/22/F6ng3AAxKc.png" title='F6ng3AAxKc.png' alt='F6ng3AAxKc.png'/>
• D.<img src="https://timg.fentiku.com/97/2016/12/22/JPqHOeBPVl.png" title='JPqHOeBPVl.png' alt='JPqHOeBPVl.png'/>

正确答案：C