thw drawing shows an apple falling to the ground. in which of the three positions does gravity act on the apple?

There is two forces acting on that Apple .

1. The Gravitational Force which is the reason why the apple falling towards the center of earth.

2. And the second less powerful force called Air drag or friction which try to keep the apple stable but Because of the power of Gravitational force and the air is not that dense so it just don't affect the apple that much as the first force does so as usual apple fall down.

Explanation: Yw.

this protocol provides a detailed procedure for co-immunoprecipitation (co-ip) to identify protein–protein interactions.