The museum will open in the spring with an exhibition and a viewing platform ___visitors can watch the big glasshouses being built.

A．what

B．where

C．when

D．why

下列说法正确的是（　　）

A．空气本来是纯净物，被污染了是混合物

B．分子与原子的本质区别是：分子比原子大

C．肥皂水可以区别硬水和软水

D．凡是均一稳定的液体是溶液