Q1: The phenomenon of collision of two elastic bodies takes place because bodies

ANS:D - all the above.

1. Immediately after collision come momentarily to rest: This may happen in an idealized elastic collision, but it's not the primary reason for the collision. After the collision, the bodies may come to rest momentarily due to the exchange of momentum, but the primary reason for the collision is the interaction of elastic forces between the bodies.
2. Tend to compress each other till they are compressed maximum possible: While the bodies may compress each other during the collision, the compression is not the primary cause of the collision. It's a consequence of the elastic forces exerted by the bodies as they interact during the collision.
3. Attempt to regain their original shape due to their elasticities: This is the correct explanation. Elastic bodies have the property of elasticity, which means they can deform under the influence of external forces but tend to regain their original shape when the forces are removed. During a collision, the bodies deform temporarily due to the forces involved in the collision, but they try to return to their original shape as much as possible once the forces are removed. This tendency to regain their original shape is a fundamental characteristic of elastic bodies and is the primary reason for the phenomenon of collision in elastic bodies.