Definition: In this task, you need to reverse all words of a given length in the sentence. The number of letters in a word determine its length. For example, the length of the word "apple" is 5.
Input: Sentence: 'looking down at skiers holding their skis on the ski slope'. Reverse all words of length '7' in the given sentence.

gnikool down at skiers gnidloh their skis on the ski slope