JEE Math Practice Question

For $$\alpha \in \mathbf{N}$$, consider a relation $$\mathrm{R}$$ on $$\mathbf{N}$$ given by $$\mathrm{R}=\{(x, y): 3 x+\alpha y$$ is a multiple of 7$$\}$$. The relation $$R$$ is an equivalence relation if and only if :

1. A.$$\alpha=14$$
2. B.$$\alpha$$ is a multiple of 4
3. C.4 is the remainder when $$\alpha$$ is divided by 10
4. D.4 is the remainder when $$\alpha$$ is divided by 7