如图甲所示，某同学在“测定玻璃的折射率”的实验中，先将白纸平铺在木板上并用图钉固定，玻璃砖平放在白纸上，然后在白纸上确定玻璃砖的界面aa
考虑以下几个问题： （1）如图15-1-3所示，参考系O′相对于参考系O静止时，人看到的光速应是多少？（2）参考系O′相对于参考系O以速度v向右运动，人
John has really got the job because he showed me the official letter ______ him it. A. offered B. offering C. to offer D. to be offered
（活动设计）生活在人民当家作主的国家，我们不仅可以依法实行民主选举、民主决策、民主管理，而且可以积极实行民主监督，为守望公共家园贡献
世界上最大的湖泊是（ ） A 贝加尔湖 B 苏必利尔湖 C里海 D巴尔喀什湖
Gina always asks_____, because her things are everywhere. A. where are her keys B. her keys are where C. where her keys are
My mother often tells me _______ my classmates when they need.A．helpB．to helpC．helpingD．helps
