There ________ a computer on my desk but there ________ two in the office.

1. A.
   is, are
2. B.
   isn't, are
3. C.
   are, is
4. D.
   are, aren't

________ is a computer on my desk.

[　　]

There ______ a computer and two boxes on my desk.

There ______ a computer and two boxes on my desk.

A．is                B．are               C．has              D．have