The pen, _____ I paid 2 dollars, was lost.

A．to which

B．for which

C．which

D．that

能证明AlCl₃为共价化合物的方法是(　　)

A．AlCl₃溶液容易导电

B．AlCl₃水溶液呈酸性

C．熔融AlCl₃不能导电

D．AlCl₃溶于水可以电离出Al^3＋和Cl^－