If I am interviewing for companies A and B, and company A makes me an offer but I don't want to commit without knowing the result of the process with company B, what is my best option?

Option 1: Accept company A, and stick with it (even if it means posteriorly having to decline a possibly better offer from company B) - this is, naturally, what I want to avoid;

Option 2: Accept company A, and if I get a better offer from company B / decide I like the position more (etc), quit from company A's offer (possibly harming the 'network' I built with them, and risking not being selected in future processes for company A);

Option 3: Tell company B I have a pending offer from another company, but that I would like to know the output of the process with them because I'm very interested in the position in company B - I am afraid that, with this option, I would be rude to company A for eventually taking to long to reply (depending on the time company B takes to act), and I am also afraid that I would seem to be lying to company B (in a 'make me an offer because the proof that I'm good is that I have another pending offer' way), therefore lowering my chances of having an offer by option B.

I am just begining my career, and therefore have zero experience with this kinds of situations, so I am very undecisive about what to eventually do.