简要回答导向机构的作用？
参考答案：
导向作用、定位作用、承受侧面受力的作用
“x＞1且y＞1”是“x+y＞2，且x•y＞1”的______条件．
Tom killed the cat. I’ll ask him why _______.
A．he did that
B．did he do that
C．he does that
D．he had done so
