Теория:

To speak about possible situations in different periods you should use Conditionals.
  
There are three types of Conditionals.
 
In each sentence there are 2 parts: the if-clause and the main-clause.
  
Type 1 Conditionals.

This type describes a real or very probable situation in the present or future.
Use these structures:

1. If + Present Simple, Future Simple ( will + V1)

If Kate works hard, she will get a high salary.
 
2. If + Present Simple, Present Simple

Water turns into ice, when the temperature falls below 0.
 
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3. If + Present Simple,  Imperative

If you don’t understand, read again the material.

4. If + Present Simple,  can/must/may + bare infinitive

If you go to London, you can see famous statues.
 
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Источники:
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