From Java SE 8, we can use static and/or default methods in interfaces, but they should be non abstract methods.
SO in this case using default in blank is completely legal.
Hence option C is correct.
Option A is incorrect as given method is not abstract, so can't use abstract there.
Options B and E are incorrect as we can't have non abstract method interface if they are not default or static.
https;//docs.oraclexom/javase/tutorial/java/Iandl/defaultmethods.html