This sentence has an error in the verb that follows a plural noun 'moose'. Option "Moose is the most important game animal in Alaska" uses a singular verb (is) in the place of a plural verb. Option "Moose, the most important game animal in Alaska" does not have any verb. Option "Mooses are the most important game animal in Alaska" uses a wrong plural form of the noun (mooses). Option "Moose have the most important game animal in Alaska" uses an auxiliary verb (have) without a main verb. Option "Moose are the most important game animal in Alaska" uses a plural verb 'are'. That is appropriate with (he) noun; hence, it is the correct answer.