图示结构中，杆b的内力N应为下列何项数值？( )

• A.N<img src="https://timg.fentiku.com/97/2016/12/22/qKykznIjc7.png" title='qKykznIjc7.png' alt='qKykznIjc7.png'/>=0
• B.N<img src="https://timg.fentiku.com/97/2016/12/22/wLXneRrwtF.png" title='wLXneRrwtF.png' alt='wLXneRrwtF.png'/>=P/2
• C.N<img src="https://timg.fentiku.com/97/2016/12/22/7HpPRBVjGB.png" title='7HpPRBVjGB.png' alt='7HpPRBVjGB.png'/>=P
• D.N<img src="https://timg.fentiku.com/97/2016/12/22/I8OkNppH1b.png" title='I8OkNppH1b.png' alt='I8OkNppH1b.png'/>=<img src="https://timg.fentiku.com/97/2016/12/22/guk2NcEZYD.png" title='guk2NcEZYD.png' alt='guk2NcEZYD.png'/>P

正确答案：A