Here are the completed sentences with the correct forms of the words in brackets:

1. He's a really **reliable** person. (RELY)
2. She made several excellent **observations** in her essay on Charles Dickens. (OBSERVE)
3. Watching TV shows in English is definitely very **useful** to improve your listening skills. (USE)
4. The Internet is probably one of the best **inventions** ever. (INVENT)
5. The boat was 16 feet in **length**. (LONG)
6. Both **accuracy** and fluency are important when speaking a foreign language. (ACCURATE)
7. You shouldn't have said that! It was a totally **inappropriate** remark. (APPROPRIATE)
8. Since the earliest times, civilisations have understood the **importance** of time. (IMPORTANT)
9. Doing puzzles keeps our brains fit and **healthy**. (HEALTH)
10. As well as gaining **satisfaction**, by doing puzzles we give our brains a good workout. (SATISFY)