As the jockey tried to ride the horse, it suddenly went berserk.

Answer: Option C

Broke : having completely run out of money.
Galloping : (of a horse) going at the pace of a gallop.
Wild : very angry.
Began : perform or undergo the first part of (an action or activity).
Berserk : out of control with anger or excitement; wild or frenzied.

Synonym of Berserk is Wild