Ecology: Competition
In ecology, competition means that several organisms need the same resource, of which there is a limited amount.
Competition can be intraspecific when the organisms are from the same species, or interspecific, when the organisms competing are from different species.
The resources can be food or water, but also territory or mates, so it applies to resources needed not only for survival but also for reproduction.
This means the right answer is A There are more living things than there are resources to support them.