Which of the Following Is an Instance of a Mortgage

Which of the following is an instance of a mortgage?

A) Richard pays Ellen $1000 a month to live in her apartment.
B) Richard pays Ellen $12, 000 a year to live in her apartment.
C) Richard gives his country estate as collateral to a bank from where he has borrowed money to buy an apartment.
D) Richard lives in an apartment for thirty years and upon his death, the apartment is transferred to somebody else.