项目质量保证包括（）
A.项目内部和外部质量保证
B.项目内部质量保证
C.项目外部质量保证
D.项目各级质量保证
参考答案：A
The doctor suggested that the old man ______ an operation without delay. [ ]
A. must have
B. to have
C. had
D. have
滚动轴承的工作温升不得超过（）℃。
A.50
B.100
C.150
