想一想,填一填。
一____城市 一____公路 一____树林
两____工程师 一____楔子 一____心
He has ______ for some years, but his _____ still makes us very sad now.
某超市有一种商品,进价为2元,据市场调查,销售单价是13元时,平均每天销售量是50件,而销售价每降低1元,平均每天就可以多售出10件.若设降价后售价为x元,每天利润为y元,则y与x之间的函数关系为( )