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: 'a cat stands next to a rocking chair in a room with floors that are covered in a thin sheet'. Reverse all words of length '7' in the given sentence.

a cat stands next to a gnikcor chair in a room with floors that are derevoc in a thin sheet