What is the missing letter?

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!
   d      g   
1. fidle

2. midle

3. wigle

4. gigle

5. pudle

6. cudle