To test the effectiveness of two Web advertising agencies, you increase your ad purchase with agency A by 50% without changing your purchase through agency B. The referrals to your website from agency A increased by only 34% but the referrals from agency B fell by 21%. What do you estimate the referrals per dollar are through agency A?

a. 1.2 referrals per dollar

b. 1.1 referrals per dollar

c. 1.0 referrals per dollar

d. 0.9 referrals per dollar