根据录音,判断句子是否正确。I didn't like dogs before,but I'm happy to have one now.
国外旅游,严禁从国外带水果等农产品,其原因是( )
将质量为0.10kg的小球从离地面20m高处竖直向上抛出,抛出时的初速度为15m/s,不计空气阻力,当小球落地时,求:
设OA→=a→,OB→=b→,则a→﹣b→=( )