The answer is B. It can be converted from high to low voltage and vice versa using transformers. That is why high voltages (tens or hundreds of kilovolts) is used to efficiently transfer electricity for large distances and then converted to 110-240V.
The answer can also be derived by elimination. [A] is not right because battery provides only Direct Current (DC). [C] is not right because high voltages are used for AC (from 110V to hundreds of kilovolts). [D] is not right because as the name Alternating Current suggests, the current is alternating in its direction. [E] is not right because DC was the first type of current invented.
