Check Boxes puzzles

Method explanation: To use the Check Boxes method, choose a box, then select a missing number from that box. Then, check the box to see if there is only one possible cell that could contain the missing number. If there is, the cell can be filled in with the missing number.

New Puzzle:
1 2 3 4 5 6 7 8 9
A
B
C
D
E
F

Using the Check Boxes method, which number goes in cell D2?

Example: