everybody was happy today,---?Yes A were they B wasn't it C

答案：C
1、这里考察的是反意疑问句的用法.
2、根据“前肯后否,前否后肯”的原则,排除AD答案.
3、主语是everyone,everybody等不定代词时,后面的主语可以用he,也可以用they.
4、以上所述,正确答案是C.