Me parece que la cuarta condicional es la zero, es decir:
--> If + simple present + simple present
Ex:
If you heat butter, it smelts.
If you put water in a cooler, it boils.
If you heat water to 100 degrees, it boils.
If you drop ice in water, it floats.
If iron gets wet, it rusts.
Espero te sirva! saludos :))
