企业销售产品时，随同产品出售单独计价的包装物，其成本计入
A、销售费用B
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设f(x,y)具有一阶偏导数，且对任意的(x,y)，
Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
Herefusedtotelluswhetherhe________(undertake)thejob.
Thedirectorrecommendedthatshe________(study)moreEnglishbeforegoingabroad.
Whenworkersareorganizedintradeunions,employersfindithardtolaythem________.
