They the habit of visiting old friends, I think is great.
A. keep on;which
B. keep up;which
C. keep on;as
D. keep up;as
网友回答
A. keep on;which
(答案→)B. keep up;which
C. keep on;as
D. keep up;as
解析：keep on有继续之意,常用于keep on doing中,keep up是维持、保持的意思。本题是“保持习惯”的意思。which与as都可引导非限制性定语从句,但在从句中作主语时常用which,且as常有“正如……,像……一样”的意思。