烧结空心砖和空心砌块（GB13545-2003）标准规定页岩烧结空心砖和空心砌块的类别代号为（）
A、N
B、Y
C、M
D、F
参考答案：B
－What do you think we can do for our aged parents?
－You_______ do anything except to be with them and be yourself. [ ]
A. don't have to
B. oughtn't to
C. mustn't
D. can't
若a＜0，则关于x的不等式ax-2＞0的解集是______．
