题干
——Do you think Peter is free today?
——__________. He is really busy preparing(准备) for the coming test these days.
A：Of course
B：I have an idea
C：1' m afraid so
D：I don' t think so
答案(点此获取答案解析）
D
、
的二元一次方
程组
的系数行列式
是该方程组有解的（ ）．
