As (something happens), (something else happens)

Use this kind of grammatical structure to describe two things that happen at the same time. It's most commonly used for two continuing processes that happen together:

As you get older, you learn what your own strengths and limitations are.

"As ___, ___" is good for describing how things work. Here's a technical description of how water boils:

As the temperature of the water rises, some of the water molecules begin to go into a gaseous state.

You can also give formal instructions using "As ____, ____":

As you leave the auditorium, please pick up one of the yellow brochures from the table by the exit.

As you begin your job search, keep in mind that there are a lot of opportunities out there; you don't have to take the first job that you're offered.

watch the gap

A "gap" is a hole or blank area between two things. There can be gaps between:

• the rooftops of two neighboring buildings
• the doorway of a train and the station platform
• a person's teeth
• rich people and poor people
• what someone remembers and what really happened

When you ride a train, you'll often hear announcements that say "watch the gap". This means that you have to be careful when you're getting off of the train, because there's some empty space bewtween the station platform and the door of the train. It's very dangerous if you fall in this gap, so you have to be careful of it.

You may also hear the phrase "mind the gap", which means the same thing.

the (train station) platform

At a train or subway station, the "platform" is the area where people stand in order to get onto the train.

You'll see the word "platform" used on elevator buttons at a train station.