问题如下：
The relationship between labor and products can be described that:
According to the above table, when L=3, the marginal product is:
选项：
A. 90.
B. 110.
C. 60.
解释：
A is correct.
When L=3, MP=90
考点： marginal product
解析：如上表所示，当L=30，边际产300-210=90
为什么不选c呢？当L＝3是，增加一单位L，产量增加60啊
