Question

Which source would most likely contain information to support the following assertion?

By sponsoring our swim team's purchase of suits and caps and allowing us to use your name on them, you will undoubtedly see an increase in sales from those on the team and their families.

surveys distributed to previous team and family members about the effect of this advertising
interviews and comments from previous donors
written testimonials or quotes from sponsors last year
all of the above
none of the above