The correct answer of the question is : B) Step-up transformer.
EXPLANATION :
Before coming into any conclusion, first we have to understand the step-up and step-down transformer.
The step-up transformer is the transformer whose transformer ratio is greater than one. It means it will increase the voltage of the source or decrease its current.
On the other hand, the transformer ratio of step-down transformer is less than one. Hence, it will decrease the higher voltage to lower voltage or increase the lower current into higher current of the given source.
As per the question, we want to increase the voltage of the source.
Hence, we have to use step-up transformer.