某种火箭被竖直向上发射时，它的高度h（m）与时间t（s）的关系可以用公式h=-5t2+150t+10表示。经过（ ）s，火箭达到它的最高点。
75
At the last moment, Tom decided to ________ a new character to make the story seem more likely.
A．put up
B．put in
C．put on
D．put off
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