换元法求积分时，换元所假设的中间变量“ t”，在最后结果中
A. 需要还原成“ x”
B. 不需要还原成“ x”
You have __________ a great deal of experience and now can work independently.
You have ________a deeper level of experience and now can work independently.
You have ________ that license unique and now can work independently.
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