What is the "it" in the sentence join them for it

In “the things they carried”, why is jimmy unsure when martha calls the pebble “a token of her truest feelings”

“third, all reviewers have a bias – no matter how impartial they try to be, opinions on movies are just that: opinions. this isn’t necessarily a bad thing: if you read a review by a critic that you know prefers foreign films, you know how seriously you should take his scathing critique of ironman.” according to this passage, all reviewers a. prefer foreign films c. have bias b. hated the movie ironman d. refuse to watch popular films

Which statement best explains the motivation for the narrator's mother to introduce her daughter to everyone they meet? from amy tan's "rules of the game."