Question

when used with the days of the week, the ____________ has the special meaning “on.”
no trabajo ____ lunes ... i don’t work on monday.
no trabajo ____ martes ... i don’t work on tuesdays.
hay una fiesta ____ miércoles ...there is a party on wednesday.
hay muchas fiestas ____viernes ...there are many parties on fridays.

Explanation:

In Spanish, when indicating "on" a specific day of the week, the preposition "el" is used for singular days and no preposition is used for plural days. In the given sentences, for singular days like "lunes", "martes", "miércoles" we use "el", and for plural "viernes" (Fridays) we don't use a preposition.

Answer:

el; el; el; el; (no pre - position for the last one as it's plural)