A.Compilation succeeds.
B.Exactly one class does NOT compile.
C.Exactly two classes do NOT compile.
D.Exactly four classes do NOT compile.
E.Exactly three classes do NOT compile.

A.public void foo（） {}
B.public int foo（） { return 3； }
C.public Two foo（） { return this； }
D.public One foo（） { return this； }
E.public Object foo（） { return this； }