在海边观察远处驶来的轮船,会出现如图中①至③所示的现象。这种现象反映的地理事实是( )
— The computer is working all the time.
— Sorry. I have forgotten ______.
____ ____ ____ study hard.
在平行六面体ABCD﹣A1B1C1D1中,化简AB→+AD→+AA1→=( )