题目

--Mr. Smith, Can you give us some advice on how to learn English well'?--Remember, Nothing can be learned well ______hard work.A．byB．throughC．withD．without 答案：D解析:略消化系统的组成包括（ ）A.消化道和消化液B.消化道和消化酶C.消化道和消化腺D.消化腺和小肠