牙体缺损最常见的原因是()
A.楔状缺损
B.龋病
C.牙外伤
D.磨损
E.发育畸形
参考答案:B
解析:5个选项所列均为导致牙体缺损的病因,但其中最常见的是龋病。
在怠速工况下测量进气管真空度,若真空表指针在45~58kPa摆动,但波动的幅度较小,则说明()。
A.配气相位错位(滞后)
B.点火时间过迟
C.配气相位错位(提前)
D.点火时间过早
John promised his doctor he________not smoke, and he has never smoked ever since.[ ]
A. might
B. should
C. could
D. would