施加预应力的目的是什么?
参考答案:
①提高结构或构件的抗裂度;
②提高结构或构件的刚度;
③充分发挥高强钢材的作用;
④把散件拼成整体。
____the book if you are free, and you will learn a lot about how to study English .
A. Read
B.Having read
C.To read
D.Reading
新生儿开始排便的时间常在生后:()
A.24h
B.36h
C.48h
D.60h
E.72h