What do we call sound waves with frequencies below 20

Theatre : Actor :: Field : ?

A # B means ‘A is the sister of B’

A @ B means ‘A is the daughter of B’

A & B means ‘A is the husband of B’

Thick : Thin :: Idle : _________

Choose the correct alternative from the given ones.

AYD, BVF, DRH, ?, KGL

World : Nation :: House : (?)

Select the number -pair from the given options that shares a similar relationship as the given number-pair.

192-108

MANDI : OXPAK :: SIRSA : (?)

Given set:  278, 257, 365

Select the option in which the numbers are not related in the same way as are the number of the following set.

(54, 23, 26)