Question

I know this isnt math related but i thought it could get answered here and i need help .

The formation of a standing wave requires?

the traveling of a wave for a long distance.

constructive interference between two waves of

slightly different frequencies.

that refraction and diffraction occur at the same time in a wave.
interference between incoming and reflected waves.

Answer 1

Not certain but I'd go with:
that refraction and diffraction occur at the same time in a wave.
interference between incoming and reflected waves.

(based on info below)

Standing waves are produced whenever two waves of identical frequency interfere with one another while traveling opposite directions along the same medium.

http://www.physicsclassroom.com/mmedia/waves/swf.cfm