In the opinion of Palmer and some other linguists of his time, _

In the opinion of Palmer and some other linguists of his time, _________ played one of the most important roles in foreign language learning.
A、grammar
B、phonetics
C、vocabulary
D、rhetoric
【正确答案】：C
【题目解析】：帕尔默和他那个时代的一些语言学家认为，词汇在外语学习中扮演着最重要的角色之一。