Explanation:

- The phrase 'sign up for sports' translates to 'kri rit vin gab'. Here, 'sign' is 'rit'.

- 'The sign post fell' is translated to 'pri dan rit nei'. We've identified 'sign' as 'rit'; thus, the remaining words are 'the', 'post', and 'fell' — 'pri', 'dan', and 'nei'.

- 'The post is closed' translates to 'dan sha fal pri'. Here, 'post' is 'dan', 'the' is 'pri'.

Based on the analysis:

- 'The' = 'pri'

- 'Post' = 'dan'

- 'Sign' = 'rit'

- 'Fell' = 'nei'

Therefore, the correct code for 'fell' is nei.