题目内容

The ratio of dry matter production to the assimilation of a particular nutrient element, usually expressed as grams per gram is called ( )

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A relationship of two organisms living together (symbiosis) and one derives its nourishment at the expense of the other is called ( )

The number of individuals of a population the environment can support is ( )

为防止砂型落砂、铸件产生裂纹和缩孔，在铸件各表面的相交处应有（）。

A. 凸台
B. 倒角
C. 铸造圆角

为了便于装配和操作安全，常在轴和孔的端部加工出一个小圆锥面，称为（）。

A. 圆角
B. 倒角
C. 退刀槽