The dog has been of most value to man in the development of ______.

A．Because the students always wore evening dress.
B．Because it wasn't evening.
C．Because all the students wore evening dress in June.
D．Because he knew she had never seen formal dress worn in the morning before.

A．Students have either a tutor or a teacher.
B．A tutor is not the same as a teacher.
C．Tutor is another word for teacher.
D．Students have a teacher as well as a tutor.