If $A=\{1,2,\{3,4\}\}$, among the following correct statements is

Option(A): 3 is not an element in A. So, $3\notin A$

Option(B): $\left\{1\right\}\subset A$ is correct because $\left\{1\right\}$ is subset to A

Option(C): $\left\{2\right\}\in A$is  is incorrect because $\left\{2\right\}\subset A$

Option(D):  $1\subseteq A$ is incorrect because $1\in A$