9. Richard his book three years ago. A wrote
B had been writing
C was writing
10. Scott different conferences before he was employed.
A was attending
B attended
C had been attending
11. How long chemical engineering?
A does Emma study
B is Emma studying
C has Emma been studying
12. Their village only renewable energy.
A has been using
B uses
C had been using
13. The students the experiment when we arrived.
A were performing
B performed
C perform
