Which of the following can be determined by using the Doppler effect? 
Definitions:
Marketing Research Project
A systematic approach to gathering, analyzing, and interpreting data related to the market and consumers to support marketing decision-making.
Churn Rate
A measure of the percentage of customers or subscribers who stop using a company’s services during a given time frame.
Subscribers
People who sign up to receive regular communications, updates, or services, often through a subscription model.
Magazine Subscription
A paid agreement to receive regular copies of a magazine, journal, or other periodical publication over a specified period.
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