题目7单选题
图示桁架(EA=常数)中,BD杆的转角为:( )<img src="https://tihai-oss-cloud.itihey.com/img/ed721c859cff4e85f4aff36915848d4a.png">A. <img src="https://tihai-oss-cloud.itihey.com/img/cebc4f04a603005cf902031a7107f487.png">B. <img src="https://tihai-oss-cloud.itihey.com/img/c145b2c0fdcd248a17dcfc82ab0d4b1b.png">C. <img src="https://tihai-oss-cloud.itihey.com/img/b27d8664ba36f08f17c0f8d1ea4dd218.png">D. <img src="https://tihai-oss-cloud.itihey.com/img/06368ac5ee6178ef4b53e82cbcb0d39d.png">