What object oriented feature can we use to have a single test program, with one set of method calls in which the user can decide which bag implementation (array- or link-based) needs testing?

The answer is "Polymorphism".

Explanation:

Polymorphism is a feature of the object-oriented programming (OOPs) language, in which data or an object is dividing into more than one form. In other words, we can say that the capacity of various objects to obtain and react in different ways is polymorphism. It enables interaction with both objects and common interfaces that hide various details of their implementation.

when earth is in rotational motion around the sun,it displaces from its place.

when a ball is placed on an inclined surface it does both the rotational and circular motion.

explanation:

the design of a ski jumping suit involves a trade-off between giving the skiers lift to get higher jumps and ensuring the skier does not face a lot of drag before the jump itself. an expansive suit may to lift the skier higher, but at the same time, it will also increase the air resistance. higher air resistance as the skier goes down the slope limits the speed of the jump. a big suit also increases the risk of losing balance or control, especially if there's a strong gust of wind. while technologically enhanced suits a lot, clothing is not the only factor in a ski jumper’s success. gathering speed while skiing down the slope, ensuring good speed on the ramp, and maintaining good body posture and form in the air all contribute to a ski jumper's success.