Fill the blank with either $in$ or $!in$ to make the statement true. $6_{3,4,7,9}$ Select the correct choice below and, if necessary, fill in the answer box to complete your choice. A$.$ The $!in$ symbol should be used because $\{3,4,7,9\}$ is a set and none of the elements in $6$ is a s $6$ B$.$ The $!in$ symbol should be used because $$ is not an element of the set. C$.$ The $in$ symbol should be used because $$ is an element of the set. D$.$ The $in$ symbol should be used because $\{3,4,7,9\}$ and $6$ are equal sets. E$.$ The