问题如下：
Business cycles are typical of economies that rely mainly on:
选项：
A.agrarian socities.
B.state enterprises.
C.business enterprises.
解释：
C is correct.
Business cycles are a type of fluctuation found in the aggregate economic activity of nations that organize their work mainly in business enterprises.
考点：Business Cycle Characteristics
解析：经济周期主要是依据一国企业的经济活动所形成的，因为一个个企业才是是经济的组成单位，所以应该选C
AB是什么呀
