______ the call for help, the boys immediately rushed out to see what was going on.

1. A.
   In order to hear
2. B.
   Hearing
3. C.
   Having heard
4. D.
   They heard

______ the call for help, the boys immediately rushed out to see what was going on.

         A. In order to hear            B. Hearing   C. Having heard       D. They heard