Final answer:
Sending a payment reminder in the form of a statement or letter when the account is 30 days past due is an appropriate collection technique.
Step-by-step explanation:
The appropriate collection technique among the given options is option c. Sending a payment reminder in the form of a statement or letter when the account is 30 days past due.
Threatening legal action (option a) and calling patients at home after 10 pm (option b) are both unprofessional and unethical practices. Option d, calling patients at work, can also be intrusive and may not be welcomed by the patients. Therefore, sending a payment reminder through a statement or letter (option c) is the best approach to collect payments effectively.