书名：14黄金认证 NEW TOEIC 新多益阅读题库解
页数：126
题目：On the first day of the class,the lab instructor demonstrated safety
procedures and warned everyone to be ___ when working with dangerous
chemicals.
(A)caution
(B)cautious
(C)cautiously
(D)cautiousness
疑问：把C删除后，但是剩下的3个选项该怎么考虑
答案是B