Which sentence uses a verb that agrees with its compound subject? a. a saw and a drill is important for a carpenter's work. b. those suitcases and this trunk have traveled many miles. c. cathy and beth takes the bus to ballet lessons. d. now either freezers or a refrigerator keep food fresh.

The answer is letter B.  
 
B. Those suitcases and this trunk have traveled many miles.     
 
The rule of subject-verb agreement is to make the subject and verb agree. If the subject is plural, the verb should also be plural. If the subject is singular, the verb should also be singular. In letter B, the compound subject “suitcases” grammatically agree with the plural verb “have”. The rest of the choices do not follow the subject-verb agreement rule at all.