Answer:
The answer is b. passive.
Step-by-step explanation:
The passive voice is used to give more importance to the object rather than the subject, in this case "The statistics" here are more important than the researcher. You can identify the passive voice often because you use: was or were, after the object, followed by the verb in the participle of the verb, and if needed, a by phrase to mention the doer. Which is this example:
- The statistics (object) were (verb to be in the past) collected (participle) by (to mention the doer) a researcher (the subject).