a) An ad group is a collection of related keywords and ads
b) An ad group is a collection of related ads
c) An ad group is a collection of related campaign settings and ads
d) An ad group is a library of your ads grouped by category
a) An ad group is a collection of related keywords and ads
Explanation: The collection of related keywords and ads is called an ad group. Each campaign can have on or more ad groups that share similar targets