Which will declare the method that forces a subclass to implement it？（）

A. The code compiles and “s=” is printed.
B. The code compiles and “s=” + s）；
C. The code does not compile because Strings is not initialized.
D. The code does not compile because Strings cannot be referneed.
E. The code comiles， but a NullPointer Exception is thrown when toString is called.

A. run
B. import
C. default
D. implement

A. foo has the value of “”
B. foo hast he falue of null.
C. foo has the value of “blue”
D. foo has the value of “green”
E. An exception is thrown.
F. The code will not compile.