研磨性外力引起的半月板损伤多见于（）
A.内侧半月板
B.外侧半月板
C.半月板中央
D.半月板边缘
E.全部半月板
参考答案：B
He _______ busy yesterday, or he _______ you with your experiment.
A．was; had helped
B．was; would have helped
C．had been; would have helped
D．were; would have helped
室内空气监测时，以下哪些属于质量保证措施。（）
A、气密性检查
B、流量校准
C、空白检验
D、仪器检验和标定
