Englishfor English speakers
once
Determiner
—
one time
We go to the house once a year.
She had only seen him once.
It's nice to be understood for once.
We get together once a month for coffee.
Not once have I said that.
—
at a time in the past, but not now
It was hard to believe that once we had been friends.
The once great city had be destroyed.
once
Preposition
—
after
Once I've finished cleaning up, we can leave.
in
Preposition
—
Used to show that something is inside something else.
The cat is in the box.
—
Used to show that someone is at home, or is available.
Is John in?
The Doctor is now in.
—
Used to show movement towards the inside.
The rain came in through the window.
a
Determinative
—
A is used when the following word could be any of a certain type.
Compare "A book I saw on the shelf" and "The book I gave you yesterday".
a
Noun
—
A is the first letter of the alphabet.
The letter "a" comes before "b".
—
In some schools, an A is a very high grade.
Ron got an A on his earth science test.