Context: Below is a food web from a tundra ecosystem in Nunavut, a territory in Northern Canada.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.
In this food web, which organism contains matter that eventually moves to the mushroom?
A. lichen
B. collared lemming
Determine the correct option from the provided choices and reply with its corresponding letter.

A