Answer
The plate and the ball should be cooled to prevent the ball from falling through the hole .
Work Step by Step
In this case, first we pay attention to the coefficient of thermal expansion of brass and aluminum.
Aluminum has higher coefficient than brass , which means it will change in volume faster than brass . If we reduce temperature , the plate will shrink more than ball so the hole will become smaller , this will prevent the ball from falling through the plate.
In the second case , if we rise the temperature , hole will expand faster than the ball , so we won't prevent it from falling through the hole.
