Here's a fun way to work on words for jobs and duties (for example, the constructions "must" or "have to"). You can do it with a friend.
"What's My Line" used to be a popular TV show in the US. The players had to guess someone's job by asking "yes or "no" questions. If they got ten "no" answers before they guessed, they lost.
To make it work for ESL, you should have an agreed list of jobs to begin--nothing rare or crazy as in the programme.
Have a look.
Answer to riddle: feet.