№17
3. has been
4. for
5. since
6. has he lived
7. for
8. have been
№18
3. I've just come home after school.
4. I've been to Saint Petersburg twice.
5. I haven't had dinner yet.
6. I've never seen a wild lion.
7. I've been doing my homework since 5 p.m..
8. I've known my best friend for 5 years.