Use the Simple Past or the Present Perfect.
1. Since classes began, I (have, not) much free time. I (have) several big tests to study for.
2. Last night my roommate and I (have) some free time, so we (go) to a show.
3. I admit that I (get) older since I last (see) you, but with any luck at all, I (get, also) wiser.
4. The science of medicine (advance) a great deal in the nineteenth century.
5. Since the beginning of the twentieth century, medical scientists (make) many important discoveries.

1 Since classes began, I hadn`t much free time. I had several big tesrs to study for.2 Last night my roommate and I had some free time, so we went to a show.3 I admit that I have got older since I last have seen you, but with any luck at all , I have got also wiser.4 The science of medicine advanced a great deal in the nineteenth century.5 Since the beginning of the twentieth century, medical scientists made many important discoveries.