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
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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.
most
Determiner
—
The majority of; much of; > 50%.
She does the most cleaning, but the least cooking.
—
The largest amount of.
Bob knows the most about cooking.
most
Adverb
—
Having the largest amount of a characteristic in a group.
You must ask yourself what is most important.
Tony is the most successful.
—
To a large degree; very.
That is most unusual.