Which of the following statements about the java.util.Vector and java.util.Hashtable classes are correct? [Check all correct answers.]
A. A Vector can hold object references or primitive values.
B. A Vector maintains object references in the order they were added.
C. A Hashtable requires string objects as keys.
D. A Hashtable maintains object references in the order they were added.
E. Both Vector and Hashtable use synchronized methods to avoid problems due to more than one thread trying to access the same collection.