---I called you last night but nobody answered.---Oh I usuallyoff my cellphone by 9:00 p

问题补充：

---I called you last night, but nobody answered.

---Oh, I usuallyoff my cellphone by 9:00 p.m.

A. switched

B. have switched

C. switch

D. had switched

答案：

A. switched

B. have switched

(答案→)C. switch

D. had switched

解析：句意：--我昨天晚上给你打电话了，但是没人接。--哦，我通常在晚上9点以后关机。因为这里指的是过去通常做某事，所以应该用一般过去时，故选C。