Which sentence shows correct use of apostrophes?

Question

The class of ’09 held its graduation ceremony at 7 o clock.

The class of 09 held its graduation ceremony at 7 o clock.

The class of ’09 held its graduation ceremony at 7 o’clock.

The class of 09 held its graduation ceremony at 7 o’clock.

Answer 1

The class of ’09 held its graduation ceremony at 7 o’clock.