[A] : Each food-level in an ecosystem is called trophic level .
[R] : When an organism benefitted with affecting the other is called commensalism .

Options

A. 1)If both A and R are true and R is the correct explanation of A
B. 2)If both A and R are true but R is not the correct explanation of A
C. 3)If A is true and R is false
D. 4)If both A and R are false