— Look! The window is broken. Someone broke it _____ purpose.

— That may be right. But perhaps it was broken _____ accident. [ ]

A. on; by

B. by; by

C. on; on

D. by; on

某课题组以苯为主要原料，采取以下路线合成利胆药——柳胺酚。回答下列问题：