Hi, I think the answer is the second option because that option sounds more reliable then the others, I am not able to determine the rest of the sentence for option 3 so this is my answer.
so crossing that bridge when you come to it is b) when you don't solve or think about any part of your life until you have to
e.g im not sure if I can do the show on Wednesdays if I get into the audition
you might not actually get into the auditions so someone else might say we'll cross that bridge/ problem when we get to it , until you get it its not relevant now.
