The question "which source is used for which campaign" is asking how many campaigns for each source.
An example answer can be:
CoolTShirts has 1 campaign for each of these sources: nytimes, buzzfeed, facebook, medium.
CoolTShirts has 2 campaigns for each of these sources: email, google
The question "which source is used for which campaign" is asking how many campaigns for each source. An example answer can be:
CoolTShirts has 1 campaign for each of these sources: nytimes, buzzfeed, facebook, medium. CoolTShirts has 2 campaigns for each of these sources: email, google