Although both gold and platinum form placers, they are not found in the same placers because:________
a. gold weathers out of felsic rocks, while platinum weathers out of mafic rocks
b. gold weathers out of mafic rocks, while platinum weathers out of felsic rocks
c. gold is soluble under reducing conditions, while platinum is soluble under oxidizing conditions
d. gold is soluble under oxidizing conditions, while platinum is soluble under reducing conditions