Here are the suitable coordinating conjunctions or conjunctive adverbs for each sentence:

1. People are very busy at work now, **so** they tend to eat more fast food.
2. You can order this laptop through this website, **or** you can go to the store to buy it.
3. The kids have to keep silent; **otherwise** they will be punished.
4. The service here is too bad, **so** we have to wait for nearly 2 hours to be served.
5. Jenny is doing her homework, **while** her brother is watching comic books.
6. My grandfather is very old; **however**, he is still healthy.
7. Nancy always tries her best at school; **for** she has been given a scholarship to study abroad.
8. This group of students is drawing, **while** the other group is making a model.
9. The test was long; **therefore** I can’t finish it on time.
10. David invited me to the cinema; **but** I was busy working.

Feel free to ask if you need further assistance!