David       his friend’s invitation to the picnic in order to stay at home and study for the test.

A. expected               B. refused              C. received

无粘结预应力砼的优点是（）

A.降低了楼层高度，提高了结构整体性能和刚度

B.不需要预留孔洞，穿筋和灌浆等工序

C.预应力筋强度能充分发挥

D.施工方便，工期短

E.锚具质量要求不高