问题补充：
It was only after I came across that matter how important it was to master a foreign language.
A. did I realize
B. had I realized
C. that I realized
D. when I realized
答案：
A. did I realize
B. had I realized
(答案→)C. that I realized
D. when I realized
解析： 考查it was…that…的强调句型。去掉it was…that后，剩下I realized how important it was to master a foreign language only after I came across that matter，是一个完整句子，所以是强调句型。选C。
