– Have they found out the _____ of the fire?

--  Yes. It was a cigarette end that _____ the fire.

--Have they found out the _____ of the fire?
--Yes. It was a cigarette end that _____ the fire

1. A.
   cause; started
2. B.
   reason; caused
3. C.
   causing; caused
4. D.
   reason; cause

     – Have they found out the _____ of the fire?

--  Yes. It was a cigarette end that _____ the fire.

A. cause; started      B. reason; caused  

C. causing; caused     D. reason; cause

   – Have they found out the _____ of the fire?
--  Yes. It was a cigarette end that _____ the fire.

―Have they found out the _____ of the fire?（ ）

―Yes. It was a cigarette end that _____ the fire.

A. cause; started　 B. reason; caused　 C. causing; caused　 D. reason; cause