The word "native" is a valid keyword, used to modify a method declaration.

Option A, D and E are not keywords. Option C is wrong because the keyword for subclassing in Java is extends, not 'subclasses'.

interface is a valid keyword.

Option B is wrong because although "String" is a class type in Java, "string" is not a keyword.

Option C is wrong because "Float" is a class type. The keyword for the Java primitive is float.

Option D is wrong because "unsigned" is a keyword in C/C++ but not in Java.