In an AdWords account managed by multiple users, one user noticed a surprising jump in impressions. Where should this user look for details on what might have created the impression increase?

In an AdWords account managed by multiple users, one user noticed a surprising jump in impressions. Where should this user look for details on what might have created the impression increase? 

A) Change History 
B) Billing Summary
C) Campaign Settings
D) Keyword Planner