Here"If" is used with present perfect tense while what I have studied
If can be used only with
1. present simple
2. simple past
3. past perfect
Kindly help in understanding this sentence

This is a good reminder that language is fluid - you don't want to be so rigid in your expectations that a simple structural change ruins your ability to tackle a question.

Typically, the If/then structure will contain the "if" clause first. For example, "If I forget to wear pants to the opera, my wife will pretend she does not know me." But it's perfectly legitimate to flip the order and write, "My wife will pretend she does not know me if I forget to wear pants to the opera."

The same is true in the OA for this question. The "then" clause comes first: "Workers cannot be laid off if they have been given reason to believe that their jobs will be safe." This is, for all intents and purposes, the same as "If they have been given reason to believe that their jobs will be safe, workers cannot be laid off."

The takeaway: do not try to memorize dozens and dozens of structures and then expect to see those structures in a form that resembles what you memorized! Yes, some rules are worth internalizing, but ultimately, you need to use context and logic, while remaining flexible enough to adapt to a variety of scenarios. Some related ideas can be found in this article.

I hope that helps!
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