--Would you like to go bike riding with us tomorrow?-Sure I am busy.A. sinceB. unless

问题补充：

--Would you like to go bike riding with us tomorrow? ---Sure, I am busy.

A. since

B. unless

C. when

D. until

答案：

A. since

(答案→)B. unless

C. when

D. until

解析：连词辨析。since 自从……以来；unless除非；when 当……时；until直到……。句意：明天你愿意和我们一起骑自行车兜风去吗?——当然了，除非我忙。故选B。