为什么钢筋和混凝土这两种力学性能不同的材料之所以能有效地结合在一起而共同工作?
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在钢筋混凝土结构中,钢筋与混凝土之间之所以能共同工作的最主要条件,就是钢筋与混凝土的黏结作用。两者之间的黏结力由哪几部分组成?
___ a new library___ in our school last year?
A. Was; built
B. Is; built
C. Does; build
Did; build
Look! A nice picture___ for our teacher.
A.is drawing
B. is being drawn
C. had been drawn
D. draws