I _____900 English words by the time I was ten.A.learned B.was learning C.had learned D.learnt

I _____900 English words by the time I was ten.A.learned B.was learning C.had learned D.learnt
I _____900 English words by the time I was ten.
A.learned B.was learning C.had learned D.learnt

I _____900 English words by the time I was ten.A.learned B.was learning C.had learned D.learnt
C
by the time I was ten 是过去完成时的标志

C
我十岁时已经会认900个英语单词了。
要用过去完成时，所以选C。

选C
到我十岁的时候我已经学了900个单词了。

C.had learned