What is missing t or th?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
   t      th   
1. sa

2. is

3. at

4. fa

5. wi

6. en

7. em