Solution:
Answer: A. $A \subset B$
Explanation:
The following information is provided in the question:
$A$ and $B$ are two examples of situations in which,
$P(A) \neq 0$
And, $\mathrm{P}(\mathrm{B} \mid \mathrm{A})=1$
$\therefore P(B \mid A)=\frac{P(B \cap A)}{P(A)}$
$1=\frac{P(B \cap A)}{P(A)}$
$P(A)=P(B \cap A)$
$\therefore A \subset B$