问题补充：
—What do you think has caused his heart attack?
—It is .
A. because of his overweight
B. due to his being overweight
C. his being overweight
D. he is so overweight
答案：
A. because of his overweight
B. due to his being overweight
(答案→)C. his being overweight
D. he is so overweight
解析：考查情景交际和省略。句意：--你认为是什么导致他心脏病发作？--是超重（导致了心脏病发作）。do you think是插入语，可忽略；问的是心脏病发作的原因，答语保留了主语，而省略了has caused his heart attack。故选C。
