How can you monitor increases in user reported Spam as identified by Google?

How can you monitor increases in user reported Spam as identified by Google?
A . Review post-delivery activity in the Email logs.
B. Review user-reported spam in the Investigation Tool.
C. Review spike in user-reported spam in the Alert center.
D. Review post-delivery activity in the BigQuery Export.

Answer: C

Explanation:

https://support.google.com/a/answer/9104586?hl=en