An advertiser wants to increase clickthrough rate (CTR). Which would help to eliminate irrelevant impressions?

An advertiser wants to increase clickthrough rate (CTR). Which would help to eliminate irrelevant impressions?
A) Assign unique keyword URLs to each keyword.
B) Evaluate the site design for improvements.
C) Add more relevant keywords to the ad group.
D) Add negative keywords to the ad group.

Answer: D