【单选题】
计算工字形梁的抗弯强度,用公式Mx/yxWnx≤f,取yx=1.05梁的翼缘外伸肢宽厚比不小于()。
①
<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191203/20191203173347_758.png"/>
②
<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191203/20191203172523_453.png"/>
③
<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191120/20191120171553_415.png"/>
④
<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191203/20191203173359_603.png"/>