线虫常用的分离方法：（）。
A.浅盘法
B.石蜡切盘法
C.肉眼观察法
D.离心法
参考答案：A
His son has poor eyesight because he plays ______ computer games.[ ]
A. much too
B. too much
C. many too
D. too many
人体内含量小于0.01%的矿物质称（）
