7. Why is the following an integral domain?
(a) ($\mathbb{Z}$, +, $\times$)?
(b) ($\mathbb{Z}_5$, $\oplus$, $\odot$)?
8. Prove the following
(a) ($\mathbb{Q}$, +, $\times$) is a field.
(b) Prove that ($\mathbb{Z}_5$, $\oplus$, $\odot$) is a field.
(c) Prove that ($\mathbb{Z}_4$, $\oplus$, $\odot$) is a not a field