Task: Question Answering
Input (English): Passage: My best friend had her birthday coming up and I decided to throw her a surprise birthday party . I asked her mother for a list of people she would want invited and then I went to the store to pick out invitations . I looked at several different invitations . I decided on the pink polka dot initiations because my friend 's favorite color is pink . When I got home I filled in all of the information about the party . The party was going to be in one week at my house . I made sure to let everyone know it would be a surprise party so my friend would n't find out about the party by accident . After I was finished doing that , I went to the post office to mail out the initiations . Question: what was the stamp put on? Option1: invitation Option2: envelope
Output (English): envelope