平面任意力系向作用面内任一点简化得到的力和力偶,其中的任何一个与原力系都不等效。
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Nina's father______(be) back in five days.
Like Hong is fond of shopping.She thinks it's a good way of ______(relax).
—How long ____ you _____ (study) in our country?—I _______(plan) to be here for about one more year.
Mary’s birthday is next Monday, her mother ______ (give)her a present.