Which expression should you use?

You have a column named TelephoneNumber that stores numbers as varchar(20). You need to write a query that returns the first three characters of a telephone number. Which expression should you use?

A.
LEFT(TelephoneNumber, 3)

B.
SUBSTRING(TelephoneNumber, 3, 3)

C.
SUBSTRING (TelephoneNumber, 3, 1)

D.
CHARINDEX(‘[0-9][0-9][0-9]’, TelephoneNumber, 3)