Emma: Hi David! How are you doing?
David: I'm fine, thanks. What about you?
Emma: I'm great! I'm calling to ask if you'd like to join us for a picnic in the park next Sunday. We're celebrating Sarah's birthday.
David: Oh, that sounds lovely, but I don't think I can make it.
Emma: Really? Why not? I thought you'd love to celebrate with Sarah.
David: I would, but _________________
Which option provides a valid reason for David's inability to attend?
A) I don't really like picnics.
B) I'm visiting my grandparents that day.
C) Sarah didn't invite me personally.
D) The weather might not be good.