A:had; have bought
B:bought; have had
C:had; have had
D:bought; have bought
在平面直角坐标系中,点P(2,﹣3)在( )
用解剖针挑取少许番茄果内制成的玻片标本叫做 ( )
下列电器中主要是利用电流通过导体产生热量工作的是( )