Englishfor English speakers
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.
lesson
Noun
—
A lesson is a time when something is taught.
The Math lesson starts at 5:12.
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.
leaving
—
noun
(= departure)
the act of departing