题目

The United States of America was founded in 1776 after the 13 independent American states rose up against the ruling British, defeated them in the American Revolutionary War, and signed the Declaration of Independence, the document which declared the creation of the new country. The men who led the revolution, drafted the Declaration of Independence, and wrote the first American laws are known as founding fathers. Benjamin Franklin, whose picture is on the US 100-dollar note, was appointed to prepare the Declaration that was eventually signed by the other founding fathers. Franklin was 下列有关电流形成的说法正确的是( )A. 电荷的移动便形成了电流B. 金属导体中自由电子发生定向移动便形成了电流C. 电路中只要接入电源便一定能形成电流D. 电流的方向总是由电源的负极流向正极