It is . . . . . . . . holiday in Europe. . . . . . . . . people have . . . . . . . . two days' holiday.

In the FIRST Blank, article "a" will be used because article "a" is used for common nouns and 'holiday' is a general term.
In the SECOND blank, article "the" will be used because 'people' in the sentence is a specific term and article "the" is used to refer to a DEFINITE thing or person.
In the THIRD blank, article "a" will be used because the speaker is making a general statement or talking about something common.