Step-up transformers are used for
The transformer is electrical equipment which transforms electrical energy (from primary side windings) to the magnetic energy (in transformer magnetic core) and again to the electrical energy (on these secondary transformer side). Thay can change (transform) the voltage of power supplied to meet the individuals needs of power consumers.
A transformer that increases voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer.
The correct option is D.