I've seen liên hệ be used with and without với. Is there a rule governing the usage of với with the verb? Is it optional?
Với in this instance means "with," though I assume the problem here was that the drop down wasn't working for you?
First choice is "to". Drop down has not been good from day one. Sometimes every choice is wrong. I would tend to rely on Tips and Notes if they bothered to put something there. The two words they have for this section means what? They slap two words and I consulted with a native speaker to confirm they are not equivalent.
I see, that is a problem. Though I will say it's best to not rely on drop downs even if they were working properly.
Prepositions in any different language will always be tricky; there will usually not be one single translation that satisfies all use cases. For instance in this sentence, English would never use "with" in such a sentence, whereas it's possible in written Vietnamese.