23.(单选题)当过度学习程度为( )时,记忆的效果最好。
No more having to buy expensive textbooks which you will only use for a year or two and then sell or _______ away.
Goods are carried by several of transport--on road or rail, by sea or air.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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