The document discusses the zero conditional, which is used to describe general facts or things that are always true. It uses the structure "if + present simple, .... present simple" to connect the condition in the if-clause with the result in the main clause. Some examples provided are: "If you freeze water, it becomes a solid"; "If public transport is efficient, people stop using their cars"; and "If you heat ice, it melts."

2. We can make a zero conditional sentence with two present simple verbs
(one in the 'if clause' and one in the 'main clause'):
If + present simple, .... present simple.
Proposición ´´if´´ (condición) Proposición principal (resultado)
´´if´´ + ´´simple present´´ ´´Present simple´´
If this thing happens that thing happens.

3. .If you freeze water, it becomes a solid.
.Plants die if they don't get enough water.
.If my husband has a cold, I usually catch it.
.If public transport is efficient, people stop using their
cars.
.If you mix red and blue, you get purple.

4. .If Bill phones, tell him to meet me at the cinema.
.If you want to come, call me before 5:00.
Meet me here if we get separated.
.If you heat ice, it melts.
.Ice melts when you heat it.
.If it rains, the grass gets wet.