Final answer:
The Time of Day report in AdWords is used to investigate whether bidding should be modified during certain hours of the day to optimize conversions.
Step-by-step explanation:
The correct answer would be d) Time of Day. The Time of Day report in AdWords allows you to analyze the performance of your campaigns at different times of the day and determine if you should modify your bidding to optimize conversions. By examining the data in this report, you can identify patterns and trends that may affect your ad performance during specific hours. For example, you may find that you get more conversions during the evening hours, and as a result, you may decide to increase your bidding during that time period to maximize your conversion rate.