Ответ:

A: Occasion: a birthday party. Janet is inviting Tina. It takes place on Sat 15 Dec at 17:30.

B: Occasion: a Halloween party / trick-or-treat event. Steve Johnson is inviting people to his house. It takes place on 31st October at 6:00 pm.

C and D: The complete invitations are cut off in the photograph, so their occasions, people and dates cannot be read reliably.