问题补充:
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
答案:
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。