Credit option strategies

This question is taken from Schweser Exam 1 # 18. The answer given however has me confused and I would appreciate someone can explain: R describes a credit option strategy that pays the holder a fixed sum which is agreed when the option is written, and occurs in the event that an issuer goes into default. R declares that this strategy can take the form of either puts or calls. My position is that the strategy can only be in the forms of puts. The answer suggest that both can work. I have read the text and cannot understand how the answer can be correct. Assistance would be appreciated

What you are saying: default of issuer = trigger for a fixed payment to owner of option. So why should only a put pay that? Don’t have that book…so not enough details…but tend to say both.