—Would you like to go hiking with us this Sunday? —Sure I am busy.A. untilB. whenC. unle

问题补充：

—Would you like to go hiking with us this Sunday?

—Sure, I am busy.

A. until

B. when

C. unless

D. since

答案：

A. until

B. when

(答案→)C. unless

D. since

解析：根据文章的意思，C符合题意。