If you were asking questions, like, how high does it go, but you don't ask when does it go to the highest point, then you don't have to go through the whole process of finding the time at which it turned around.

如果你想问,例如,它可以到多高,不过你并没有问它何时达到最高点,那么你不用从头到尾再来一遍,来弄清质点何时转向

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