A financial institution sent messages about strong financial habits to two groups. Group A received the messages via email on a weekday morning. Group B received the messages via the bank's app when they signed in. What was the institution trying to determine with their A/B testing?

A. How many customers use email.

B. The best method to reach their customers about financial habits.

C. How many customers already had good financial habits.

D. Whether a customer who used a banking app was likely to have strong financial habits