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.

Sentence: 'a couple of elephants that are in some water'. Reverse all words of length '6' in the given sentence.
a elpuoc of elephants that are in some water

Sentence: 'a red pair of scissors on top of an envelope'. Reverse all words of length '2' in the given sentence.
a red pair fo scissors no top fo na envelope

Sentence: 'a person that is flying a kite in the air'. Reverse all words of length '6' in the given sentence.

a nosrep that is gniylf a kite in the air