Unlike regulators in Europe who aim to prevent airlines from building monopoly positions at European airports, in America there are no such endeavors, as evidenced by the fact that at 40 of America’s 100 biggest airports, a single airline accounts for more than half the capacity of the airport.
A. Unlike regulators in Europe who
Incorrect comparison being made between "regulators" and "in America". Eliminate.B. Whereas in Europe regulators
Correct answer - "in Europe" is being compared to "in America" and no fresh errors are introduced. C. Whereas European regulators who
Same error as (A). Eliminate.D. Although in Europe regulators
This is a tempting option as it is structured very similar to option (B). However, by using "although" one tends to expect some sort of a contrasting effect in the rest of the sentence. When comparing with another country/region, "whereas" brings out the difference better. Overall, because of the presence of option (B), we can eliminate option (D).E. Even though European regulators
Same error as (A) and (C). Eliminate.Hope this helps.