She gets up early … the weekdays.

(a) at
(b) of
© on
(d) in

This test is concerned with the preposition problem and the correct answer is ©, but I would like to call your attention in other respects: Is “the” correctly used in the sentence?

  As far as I know "[i]at the weekend[/i]" is considered to be fixed expression, in which "the" cannot be omitted. Am I right? What about [i]on (the) weekdays[/i]?


You are right. ‘The’ is not needed in your sentence because ‘weekdays’ is not specified but referred to in a general sense.