There are two main sets of Games — the Winter and the Summer Olympics, and both are held every four years on a basis.
A. valuable
B. former
C. regular
D. swift
网友回答
A. valuable
B. former
(答案→)C. regular
D. swift
解析：A．valuable有价值的，B．former以前的，C．regular定期的，有规律的，D．swift迅速的，句意：有两个主要的运动会—冬奥会和夏季奥运会，两个都是每四年举行一次。根据句意选C。