Multiple newspapers ______ blank the Spanish-speaking population of Washington, DC, including El Tiempo Latino and

Choice A is the best answer. The convention being tested is the use of verb forms within a sentence. A main clause requires a finite (tensed) verb to perform the action of the subject (in this case, "multiple newspapers"), and this choice supplies the finite present tense verb "serve" to indie that there are multiple newspapers serving the Spanish-speaking population of Washington, DC.

Choice B is incorrect because it results in an ungrammatical sentence. The nonfinite participle "having served" doesn’t supply the main clause with a finite verb. Choice C is incorrect because it results in an ungrammatical sentence. The nonfinite to-infinitive "to serve" doesn’t supply the main clause with a finite verb. Choice D is incorrect because it results in an ungrammatical sentence. The nonfinite participle "serving" doesn’t supply the main clause with a finite verb.