A
It steps up the voltage and steps down the current.
Explaination
The basic operation of a transformer is to step up or step down the voltage in the circuit. If the transformer is a step up then it will step up the voltage and step down the current to maintain the power (i.e. P=VI) in primary and secondary sides of the circuit.
B It steps up the voltage.
C It steps down the current.
D It steps up the current.