洁净室压力:洁净室与室外至少保持()的正压。
参考答案:10Pa
Peter! Don't read _________ bed. It's bad _________ your eyes.[ ]
A. in the; for
B. in; for
C. on; with
D. on the; with
两物体甲和乙在同一直线上运动,它们在0~0.4 s时间内的v-t图象如图所示。若仅在两物体之间存在相互作用,则物体甲与乙的质量之比和图中时间t1分别为
A.和0.30s
B.3和0.30s
C.和0.28 s
D.3和0.28 s