1. They () about snorkeling for a month so they were ready for their first attempt.

    had learned

    had been learning

2. Mary wasn't able to swim because she () her arm.

    had injured

    had been injuring

3. John () zorbing before so he was a bit nervous.

    had not done

    had not been doing

4. They () down the mountain for a while when suddenly an avalanche put their lives in danger

    had skied

    had been skiing

5. James couldn't go scuba-diving because he () his equipment.

    had forgotten

    had been forgetting

6. They () for some hours when they decided to have a break and have something to eat.

    had hang-glided

    had been hang-gliding