* Biotic factors are living organisms or the products of living organisms.

* Acorns are the fruit of oak trees, making them a product of a living organism.

Here's why the other options are abiotic (non-living):

* 1) Stream - A stream is a body of water, a physical feature.

* 2) Rocks - Rocks are geological formations, not living.

* 4) Carbon dioxide - Carbon dioxide is a gas, a chemical compound.