According to an answer from another and a bit of my own research;
A decomposer is exactly what it sounds like, an organism that decomposes something and feeds off of it. You can eliminate the answers "Owl" and "Hawk" from a first glance as they are both consumers. Looking at it again, an "Ant" is not a decomposer, but rather, a consumer just like your other two options. This leaves "Fungus", something that decomposes it's food.
Please forgive me if I'm wrong. Feel free to ask for more information and I will scour the internet to see what I can find. <3
[bloominginthedark/bloom]