---James is good at sports. He plays ______ basketball well,

and he plays ______ piano well, too.

--- Wow, he’s so great!

A．the, the

B．/, /

C．/, the

D．the,

( )订立合同时并非有效，被追认后有效。

A．可撤销合同

B．可变更合同

C．无效合同

D．效力待定合同