Place one ball on top of the other so that the balls are touching and hold at arm’s length.

Drop the balls at the same time. What

happens?

The two balls separate from each other.

Explanation:

If we place one ball on top of the other so that the  balls are touching each other and hold at arm’s length and we drop these two balls at the same time, the first ball which touches the ground is the lower one and after touching the ground, the  ball is pushed upward by the ground due to reaction and the lower ball moves upward covering little distance from the ground and the upper ball also moves upward because the force is transferred from lower ball to the upper ball and the upper ball detached from the lower ball and the two balls separate from each other.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.