Sure, here are the completed sentences:

1. My dad couldn't **go** to work because he was ill.
2. John couldn't **find** his pen. It wasn't in his school bag.
3. Mary wasn't hungry—she couldn't **finish** her lunch.
4. I couldn't **understand** Jane because I don't speak German.
5. We couldn't **hear** the teacher because the students were very noisy.
6. Tom couldn't **listen** to music because his CD player was broken.
7. I was very tired but I couldn't **sleep**.
8. We couldn't **play** tennis because the weather was bad.

The extra words are **love** and **speak**.