문제 내용: 밑줄 친 부분 중 어법상 옳지 않은 것은?
선택지 1: which the first modern electric battery was developed
선택지 2: were ideal for producing an electrical current
선택지 3: called a Voltaic pile, was made by stacking some discs
선택지 4: such talk about Volta's work that he was requested to conduct a demonstration