Bunuel wrote:
Whether brick-and-mortar bank locations will survive
this era of online payments and digital transfers are debatable.
A. this era of online payments and digital transfers are debatable
B. in this era of online payments and digital transfers are debatable
C. is debatable in this era of online payments and digital transfers
D. this era of online payments and digital transfers are being debated
E. have been under debate in this era of online payments and digital transfers
VERITAS PREP OFFICIAL SOLUTION:
This problem comes down to one major decision point: subject-verb agreement. If you notice that choices A, B, D, and E all have plural verbs (are, are, are, and have been), and that only choice C uses the singular "is," you can quickly find the subject of the sentence. What is being debated? Whether banks will survive, and "whether" is a singular subject. Therefore you need a singular verb, and only choice C provides that.
Note that one way in which the GMAT testmaker makes subject-verb agreement difficult is in the use of "nontraditional" subjects. Here that manifests itself with "Whether banks will survive" as a subject, and in other questions it might be "however much the parties may agree" or something of that kind. Be on the lookout for situations, as opposed to classic nouns, as subjects on difficult Sentence Correction problems.