晚期囊胚透明带消失后，相当于受精后第几日开始着床
A．2～3天
B．4～5天
C．6～7天
D．8～9天
E．10～11天
参考答案：C
Tony used to _______ to school, but he is used to _______ to school now. [ ]
A. walk; taking a bus
B. walked; took a bus
C. walk; take a bus
预应力筋的张拉，0→初应力理论计算伸长值为2cm，初应力→控制应力的实测伸长值为22cm，则预应力筋的张拉伸长值为( )cm。
A．24
B．20
C．22
D．26
