—Look! More trees are being planted around the new building. What do you think of ________natural surroundings here?

—Fantastic! Beyond _______ expression.

A．the; 不填

B．the; the

C．不填; 不填

D．the ; an

有利于减少吸附和吸留的杂质，使晶形沉淀更纯净的选项是（）

A、沉淀时温度应稍高 

B、沉淀时在较浓的溶液中进行 

C、沉淀时加入适量电解质 

D、沉淀完全后进行一定时间的陈化