If a ball is rolling in a straight line and you push it to the right, its velocity will to the right.
a. displace
c. frame
b. accelerate
d. reference

It's velocity will Accelerate, to the right as (if you exclude momentum which makes the law weird) Newton's 2nd law states that the resultant force on an object is proportional to its acceleration and always in the same direction as the acceleration. Therefore, a force pushing an object to the right will cause an acceleration to the right.

The answer should be a.