Which TWO of the options below make up the list of four?

Barney (1991) identified four criteria necessary for a resource to be classed as unique and thus give competitive advantage. One of these is that it shouldn’t be substitutable and another is that it should be rare.

Which TWO of the options below make up the list of four?
A . Valuable
B . Imperfectly Imitable
C . Perfectly Imitable
D . Costly to obtain

Answer: A,B