Refer to the figure below. The opportunity cost of increasing medical care from 200 to 400 units is __ the opportunity cost of increasing medical care from 400 to 600 units.

Refer to the figure below. The opportunity cost of increasing medical care from 200 to 400 units is __ the opportunity cost of increasing medical care from 400 to 600 units.
A.twice as much as
B.less than
C.exactly the same as
D.greater than
正确答案：less than