下列操作达不到预期目的是（　　）

①石油分馏时把温度计插入受热的液体中  

②用酸性高锰酸钾溶液除去乙炔中含有的H₂S

③用乙醇和3%的硫酸共热到170℃制取乙烯 

④将苯和溴水混合后加入铁粉制取溴苯

⑤将敞口久置的电石与蒸馏水混合制乙炔．

A．只有①⑤

B．只有③④⑤

C．只有①②③⑤

D．①②③④⑤

_____ he used to play a lot of computer games, but now he seems to have lost interest in them. [ ]

A. At a time

B. At one time

C. At all times

D. At the same time