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 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: 'an elephant is standing in the road by the truck'. Reverse all words of length '5' in the given sentence.
an elephant is standing in the road by the kcurt

Sentence: 'teenage boys are playing a video game in a crowded area'. Reverse all words of length '2' in the given sentence.

teenage boys are playing a video game ni a crowded area