Question

【题目】By the time he was 4 years old, he ________ 100 English words.

A. learns B. will have learned C. has learned D. had learned

Answer 1

【答案】D

【解析】

考查过去完成时。句意：到他4岁的时候，他已经学会了100个英语单词。by the time引导的时间状语从句，从句过去时，主句用过去完成时。故D选项正确。