State whether the following set is finite or infinite:
The set of lines which are parallel to the $x$-axis.

Which of the following sets is a subset of all other sets?

Show that the following four conditions are equivalent:
$(i) A \subset B, \quad (ii) A - B = \phi, \quad (iii) A \cup B = B, \quad (iv) A \cap B = A$

Find the union of each of the following pairs of sets:
$A = \{1, 2, 3\}, B = \varnothing$

Let $A = \{1, 2, \{3, 4\}, 5\}$. Which of the following statements is incorrect and why?
$1 \subset A$

Let $A = \{1, 2, 3, 4, 5, 6\}$. Insert the appropriate symbol $\in$ or $\notin$ in the blank space:
$8 \dots A$