单选题 Although he ______ mentioned the introduction of that product, his remark still has a profound effect on his fellows.
A. once
B. besides
C. still
D. yet

【正确答案】 A
【答案解析】高级问题 空格内应填入副词。所有选项都可做副词使用,但词义上最合适,并且能和过去时搭配的只有once。once当连词用的时候是“一旦……”的意思,引导条件状语从句。
[高频词语] besides (prep. ; adv.) 此外,加之 still (adv.) 仍然 yet (adv.) 尚,还;(conj.) 然而