—Watch!

—I ____ but ____ I ____ anything unusual.

A．watched; have watched

B．have watched; am not seeing

C．was watching; wasn’t seeing

D．am watching; don’t see

水下混凝土灌注对混凝土和易性要求较高，故混凝土的砂率宜为（）。

A．20%～30%

B．30%～40%

C．40%～50%

D．50%～60%