We note that $19^{2} \equiv 1$ $( \text{mod} \textbackslash; 4)$ and hence:  $19^{2021} \equiv 1^{1010} \times 3 \equiv 3$ $( \text{mod} \textbackslash; 3)$ 
What is the remainder when we divide $19^{2021}$ by $4$? 
a) $$0$$ 
b) $$1$$ 
c) $$2$$ 
d) $$3$$ 