The national insurance firm offers four tiers of coverage plans;
buyers can choose among bronze, silver, gold, and platinum plans, there are no plans that offer greater coverage than the platinum tier or less than the bronze.
(A) buyers can choose among bronze, silver, gold, and platinum plans, there are
This sentence looks like a run-on sentence, so that's why it's incorrect.(B) because buyers can choose bronze, silver, gold, or platinum, there are
We can't use "because" here, it's incorrect.(C) however, buyers can choose among bronze, silver, gold, and platinum, and
"however" doesn't make sense here so that's why it's wrong.(D) buyers can choose among bronze, silver, gold, platinum plans, but
The problem is that there's no "and" between gold and platinum so that pushed me away.(E) although buyers can choose among bronze, silver, gold, and platinum plans, there are
yea, this seems reasonable. Although I am not happy with "although", I am ok with it. 
Answer is E.