AMC 12 2016b Problem 12

All the numbers $1, 2, 3, 4, 5, 6, 7, 8, 9$ are written in a $3\times3$ array of squares, one number in each square, in such a way that if two numbers are consecutive then they occupy squares that share an edge. The numbers in the four corners add up to $18$. What is the number in the center?

\textbf{(A)}\ 5 \textbf{(B)}\ 6 \textbf{(C)}\ 7 \textbf{(D)}\ 8 \textbf{(E)}\ 9