Answer: D. Online survey
Explanation: Interview survey is time consuming and John does not have the luxury of time. Phone survey is fast but needs money and John is cash trapped. Longitudinal survey requires that a long time is spent on the survey and it is expensive. John does not have both the time and money. Mail survey is cheap but needs time to get in the answers and John does not have much time. The best option for John is online survey because online survey are less time consuming, cheaper, and results gotten faster.