One of your clients wants to know why a campaign went over the specified daily budget

The question is incomplete and here is the complete one with the choices:

One of your clients wants to know why a campaign went over the specified daily budget several days in a row. What would you explain to your client about how the AdWords system works?

A) AdWords automatically increases the maximum cost-per-click (CPC) bid to show an ad higher in Google search results

B) Due to changes in traffic, AdWords allows up to 20% more impressions in a day than the budget specifies

C) To show an ad more often, AdWords charges more than the average daily budget amount multiplied by 30.4

D) Due to changes in traffic, AdWords allows up to 20% more clicks in a day than the budget specifies. However, in any given month, AdWords never charges more than the average daily budget amount multiplied by 30.4

The correct answer for this is option "D"

In an easy way to explain the option, if someone’s ads are run in a frequent manner the budget might cross the daily limit up to 20 percent but this will not be affecting the total monthly budget multiplied by the average number of days in a month (30.4).