问题补充:
It was not until then that I came to know that knowledge only from practice.
A. had come
B. has come
C. came
D. comes
答案:
A. had come
B. has come
C. came
(答案→)D. comes
解析:主句虽然是过去时态,但从句所说明的是不受时间限制的真理或事实,名词性从句的谓语动词仍然用一般现在时。又如:He said Asia is the largest continent.