Answer: C) I interviewed a local scientist.
Step-by-step explanation: an independent clause is a phrase that has a subject and a predicate, and that can stand by itself and make complete sense. In the given sentence, the independent clause is the corresponding to option C: I interviewed a local scientist, the subject is "I" and the predicate is "interviewed a local scientist." The rest of the sentence "because I needed stronger support for my essay" is a subordinate clause.