<span>Calling
up experts and setting them up in interviews is the most reliable way to get
the opinions of experts on any writing topic. Because in this type of source,
you get the first-hand information from someone who has a forte on that certain
area.</span>
I believe it is c because you use a comma after a conjunction and in b and d the phrase that is in the commas doesn't stand alone/ the sentence cant stand without it
I'd say its the second choice
The answer is b perspective