Sara read in a book that in 1800, the Italian physicist Alessandro Volta observed that two metals connected by a conducting liquid produced a continuous transfer of electrons. This phenomenon was different from the rapid static discharge observed by Benjamin Franklin.
Sara’s book was describing Volta’s observation of:

The correct answer is option C, electric current

Electric current is due to the flow of electrons. In this case the two metal rods act as electrodes with in a conducting liquid. A chemical reaction takes place at the electrodes due to which free electrons are released. These electrons starts traveling from the region of high negative potential to the regions high positive potential through the connector connecting the two electrodes thereby producing electric current.