题目

俗话说：“种瓜得瓜，种豆得豆。”控制这一现象的物质主要存在于下列哪一结构中（  ） A.细胞膜             B.细胞核         C.液泡           D.细胞质 答案：B23．— What’s that terrible noise．David? — Oh，I forgot to tell you．The new machines in the nearby plant _______．A．were testedB．will be testedC．are being tested D．have been tested