18. It was because of English girlfriend, believe it or not, his English improved so greatly.
A. which
B. as
C. that
D. what
网友回答
A. which
B. as
(答案→)C. that
D. what
解析：为强调句型，被强调成分为 because of English girlfriend。由于句中插入了believe it or not这一成分，致使许多同学误认为这是一个非限制性定语从句。