Which of the following are sets ? Justify your answer.

A collection of novels written by the writer Munshi Prem Chand.

Which of the following are sets ? Justify your answer.

The collection of all boys in your class.

In the following state whether $A=B$ or not :

$A=\{a, b, c, d\} ; B=\{d, c, b, a\}$

Let $A=\{a, e, i, o, u\}$ and $B=\{a, i, u\} .$ Show that $A \cup B=A$

Let $A, B,$ and $C$ be the sets such that $A \cup B=A \cup C$ and $A \cap B=A \cap C$. Show that $B = C$

State whether each of the following set is finite or infinite :

The set of letters in the English alphabet