Hint for Text completion

While doing Text completion question, I am not able to figure out what is the hint/clue to fill up the blank. Not the support/contrast concept but how the word ‘by decade’ from the below question is used to fill the blank.

Is there any specific video(s) which talk about it? How to identify the word/phrase present in the text that could help us identify the blank.

Which blank are you referring to?

I am referring to the first blank. ‘by decades’ is the clue used to fill the first blank.

However, I am not asking about this particular question. I am asking about strategy to identify hints. Like greg used ‘by decades’ to suggest that the first blank would be a term like chronic or prolonged.

Temporary is an incorrect guess

Can you suggest if any particular recording exists dedicated to this concept.

If you’re not sure what to focus on, try and figure out the specific function of the blank within its own idea:

Blank 1: describes the nature of the problem where teachers are not respected

Now you can look for any clues that can do this