That wolf-after reading the sentence, it is clear to see we have a complete main verb and subject. after the blank, there seems to be another verb followed by a full predicate. therefore, we might anticipate some form of connector and subject.
it is not letter d because there is no comma before the blank, and the global idea is not about a consequence. it is not letter c because in this sentence the connector has a meaning conflict with the subject. it is not letter a because there is no comma before the blank and the idea is not conveying and addition. the correct answer is letter b.