On which tab can advertisers see credits for invalid clicks within their AdWords accounts?



On which tab can advertisers see credits for invalid clicks within their AdWords accounts?
A) Opportunities
B) Billing
C) My account
D) Campaigns

In addition to our automatic filters (which will catch and discard the vast majority of invalid clicks), our team proactively identifies invalid activity that may not have been automatically filtered and credits advertisers accordingly. These credits used to appear on your Billing Summary page as 'Service Adjustments.' In the interest of transparency, all credits, past and future, for invalid click activity are now labeled 'Adjustment - Click Quality.'
You may notice these credits appearing more frequently as we work hard to ensure that this advertising budget is returned to affected advertisers as quickly as possible.

Tư liệu tham khảo:
http://adwords.blogspot.com/2006/03/invalid-click-credits.html
http://adwords.blogspot.com/2006/03/about-invalid-clicks.html
https://support.google.com/adwords/answer/42995