in the if clause, when we want to expess something real or possible, we use the present like present continuous, present perfect and simple present. so, I would be very happy if you can help me to come clear about how different the three above present tenses are. which situation can we use one of those?
You are about to visit Eleanor. You tell your friend. Your friend says to you:
1. If Eleanor eats an egg, tell her to try this tomato too.
2. If Eleanor is eating an egg, tell her to try this tomato too.
3. If Eleanor has eaten an egg, tell her to try this tomato too.
In #1 (present simple), the proposed action ("eating an egg") may happen at any time after your arrival.
In #2 (present progressive), the proposed action is in progress at the time of your arrival.
In #3 (present perfect), the proposed action has already occurred, at the time of your arrival.
Thus the choice of form expresses the relation of the action to the time of your arrival.
Let me know if it's still unclear!
All the best,
Not a professional ESL teacher.