They were determined to carry out the plan at first, but then we ________ persuade them to

change their minds.[      ]

A. would  

B. could

C. were able to  

D. had to

下列处置、操作或现象的描述中正确的是（　　）

①有大量的氯气泄漏时，应用浸有弱碱性溶液的毛巾捂住口鼻向高处跑

②用托盘天平称量50.56g KCl，0.56g通过移动游码来实现

③金属钠着火燃烧时，用泡沫灭火器灭火

④让一束光通过胶体，可以看到一条光亮的“通路”

A．③④

B．②④

C．①④

D．①③