In a solar cell, semiconductors of the p-type and n-type are placed in contact with each other via a conducting wire. in order to generate an electric current, which of the following must be true? a. an external battery must be attached b. light shining on the system will cause oxidation to occur c. light shining on the system must have enough energy to set electrons in motion from the ntype semiconductors to the p-type d. light shining on the system must have enough energy to set electrons in motion from the ptype semiconductors to the n-type