Easy# Open, Closed, Compact in Complete Metric Space

TOPO-JKYWCX

Let $X$ be a complete metric space, and let $A\subset B \subset X$, where $A$ is an open set, and $B$ is a closed set.

Recall that $K$ is a *compact subset* of $X$ if for every sequence $(x_n)_n$ in $K$ there exists a subsequence $(x_{n_k})_{k\geq 1}$ which converges to a point in $K$.

Pick the correct statement from the list: