Compasses are not often used in our maths class．However, _________ is often used．

1. A.
   a compass
2. B.
   a pair of compass
3. C.
   a pair of compasses
4. D.
   compass

Compasses are not often used in our maths class．However, _______ is often used．

A．a compass                                              B．a pair of compass 

C．a pair of compasses                                D．compass．