Which of the following can't be used to make a solar cell?

Silicon Platinum Gallium Germanium

Platinum

Solar cells generally require semi-conductors for their construction.Silicon and Germanium are semi-conductors and Gallium when mixed with other impurities can act as semi-conductor but Platinum is not a semiconductor and Platinum being a metal is a good conductor .It can not be used as semi-conductor and more over platinum is very expensive to get.