All the numbers 1,2,3,4,5,6,7,8,9 are written in a 3 \times 3 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 number is in the center?

**Answer Choices**

A. 5

B. 6

C. 7

D. 8

E. 9