Botanists recognize over fifty different species of sunflower. One species, the silverleaf sunflower, ______ blank both

Choice D is the best answer. This verb needs to function as the main verb in the sentence, with the subject “one species,” so it needs to be conjugated. This choice gives us the singular present tense “includes,” which is the only conjugated form of the verb among the choices. 

Choice A is incorrect. This doesn’t complete the text in a way that conforms to the conventions of Standard English. This verb needs to function as the main verb in the sentence, with the subject “one species,” so it needs to be conjugated. “Having included” is a participle form of the verb: it’s not conjugated and doesn’t function like a normal verb. Choice B is incorrect. This doesn’t complete the text in a way that conforms to the conventions of Standard English. This verb needs to function as the main verb in the sentence, with the subject “one species,” so it needs to be conjugated. “Including” is the gerund form of the verb: it’s not conjugated and doesn’t function like a normal verb. Choice C is incorrect. This doesn’t complete the text in a way that conforms to the conventions of Standard English. This verb needs to function as the main verb in the sentence, with the subject “one species,” so it needs to be conjugated. “To include” is the infinitive form of the verb: it’s not conjugated.