good habits very important.A. Having; isB. Having; areC. Have; isD. Have; are

问题补充：

good habits very important.

A. Having; is

B. Having; are

C. Have; is

D. Have; are

答案：

(答案→)A. Having; is

B. Having; are

C. Have; is

D. Have; are

解析：考察动名词做主语。养成好习惯这一件事做主语，谓语用单数。故选A