List all the elements of the following sers :

$F = \{ x:x$ is a consonant in the Englishalphabet which precedes $k\} $

What universal set $(s)$ would you propose for each of the following :

The set of right triangles

Which of the following are examples of the null set

Set of odd natural numbers divisible by $2$

In each of the following, determine whether the statement is true or false. If it is true, prove it. If it is false, give an example.

If $x \in A$ and $A \in B,$ then $x \in B$

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 $B = C$