Birds, squirrels, and chipmunks all living in the same tree, using the same resources, are an example of:

Explanation :  

In Interspecific competition, different individuals of different species fight for the same resource in an ecosystem. The resources can be food or living space.

Birds belong to the group of aves, squirrels and chipmunks are from the family of Sciuridae.  

All three are from different species. They are on the same ecosystem i.e. tree. They form the interspecific competitions.

c) up is the direction the magnetic force is acting on the charge.