Which statement best describes a situation where competition occurs in an ecosystem?
(1)a deer outruns an attacking wolf.
(2)a deer, during the winter, consumes tree bark.
(3)a deer and a rabbit consume grass in a field.
(4)a deer and a rabbit are both startled by a hawk flying overhead.

Option C

Explanation:

A competition with in an ecosystem usually occurs among the species for limited resources such as food, habitat, etc.

Of all the given options, Option C clearly indicates that both the deer and rabbit depend on the same resource i.e grass for feeding themselves. Over a time period when production of grass would reduce, there can be a competition between these two species for food.  

Hence, option C is correct

d. sodium chloride ions.