Dan Owns a House That Was Mortgaged to First Bank

Dan owns a house that was mortgaged to First Bank.Dan purchases a central air conditioning unit in January 2011, from Bob's Appliances on credit and gives Bob's a security interest in the unit.In most states, in order to gain priority over First Bank, Bob's Appliances must:

A) perfect by a fixture filing.
B) perfect within 20 days after the unit is installed.
C) notify First Bank in a letter of his security interest before the unit is installed.
D) two of the above.(a and b)
E) none of the above.