上升极限位置限位器失效时，司机应靠经验准确操作。（）
A、正确
B、错误
参考答案：B
在第四脑室塑型生长的肿瘤是
A．小脑髓母细胞瘤
B．小脑星形细胞瘤
C．四脑室室管膜瘤
D．脑膜瘤
E．血管网状细胞瘤
— My parents are getting old. What can I do for them?
— You _____ do anything except to be with them more. [ ]
A. oughtn't to
B. don't have to
C. mustn't
D. can't
