A:I go to school at a quarter to seven.
B:I go to school at a quarter to eight.
向量a→=2,3在向量b→=3,-4上的正射影的数量为( )
下列有关基因的叙述,不正确的是( )
在物理学研究中,有时可以把物体看成质点,则下列说法中正确的是( )
—How was your recent trip to Sichuan? —I've never had_______ one before.