could just explain what "excluding as unacceptable one obvious alternative" means? On my first read through I didn't really understand it

i felt the exact same way. I had to re-read that answer choice again to fully comprehend.

Hello! After struggling to answer the same question, I realized what I was not understanding from answer choice C and how it related to the conclusion ("so the only acceptable solution is to fine burglar alarm system owners the cost of 45 minutes of police time for each false alarm their systems generate."). Basically, after stating that false burglar alarms are bad, the argument pivots to mentioning a positive then provides that the *ONLY ACCEPTABLE* solution to the problem is to fine alarm owners for the 45 minutes. So, the part mentioned in the question stem is the premise, or basis, on which only one acceptable solution is provided (i.e. all other solutions are unacceptable). This could otherwise be translated into, "excluding as unacceptable one obvious alternative."