Select the most more appropriate option to fill in the blank.

Did the boys turn ________ for football practice?

up

The most appropriate option to fill in the blank is up.

The word "up" means to arrive at a place or to be present at a certain time. In this context, it is the most accurate word to describe what the boys did for football practice. The boys turned up for football practice. They arrived at the football field at the appointed time and were ready to practice.

The other options are not as appropriate.

• On means to be in contact with or close to something. The boys did not turn on for football practice. They did not turn on the lights or the equipment.
• Back means to return to a previous place or state. The boys did not turn back for football practice. They did not turn around and go home.
• In means to enter a place or to be included in something. The boys did not turn in for football practice. They did not turn in their homework or their uniforms.