Lila Has Created a Display Campaign to Help Support Her

Lila has created a display campaign to help support her consulting business. The ad has been running for six months. Her goal of the campaign is to get people to sign up for her newsletter. If Lila has a desire to get more conversions at a lower cost, which Google AdWords tool should she use?

A) My Change History tool
B) Conversion optimizer
C) Display ad builder
D) Keyword tools