Here is an exercise in which some blanks have been given to be filled with the following collective nouns. I've tried my best but there seems to be some mistakes.
So, I'd be so thankful for any correction in advance:


1. A flock of sheep
2. A gang of thieves
3. A bunch of grapes
4. A bouquet of flowers
5. A staff of teachers
6. A pack of cards
7. A    ?     of stairs
8. A swarm of flies
9. A range of mountains
10. A herd of cows
11. A team of footballers
12. An audience at a lecture 


You simply did not write in the remaining term by default:

7. A flight of stairs
Students: We have free audio pronunciation exercises.
Hi MM,

Thank you very much.
YES. You're right. I didn't notice. How about the others? are they right?


Yes, they are all right.