A. Politicians and economists are reluctant to question the presumptions of Global Free Trade and are fail to confront or even comprehend its effects on a world economy that is changing radically. -- Incorrect. The 2nd element in the parallel construction is not parallel to the first element. 1st element :: P&E are X, X is a adjective phrase. 2nd element i.e. "are fail to.. action 1 or even action 2" is an attempt at verb marker. Incorrect.
B. Politicians and economists are reluctant to question the presumptions of Global Free Trade and fail to confront or even comprehend its effects on a world economy that is changing radically. -- No error. Keep it. Correct answer (after review of all other choices)
C. Politicians and economists are reluctant to question the presumptions of Global Free Trade and are failing to confront or even comprehending its effects on a world economy that is changing radically. -- Same as A. Elements ought to be parallel are not parallel.
D. Politicians and economists are being reluctant to question the presumptions of Global Free Trade and fail to confront or even comprehending its effect on a world economy that is changing radically. -- "being" is only used to demonstrate a temporary state. Usage here is not appropriate. Eliminate.
E. Politicians and economists are going to be reluctant to question the presumptions of Global Free Trade and fail to comfort or even comprehend its effects on a world economy that is changing radically. -- Eliminate. "noun" (gerund) and "verb phrase".