二次浇灌的地脚螺栓，须待混凝土干燥牢固后，混凝土强度达到( )才能拧紧，否则影响安装质量。
A．50%
B．75%
C．85%
D．100%
参考答案：B
场独立性与场依存性各自的优势是什么
Most of the evidence was destroyed in the fire. ______, it would be almost impossible to prove Jim guilty.
A．Anyhow
B．Thus
C．However
D．Besides
