Thesub-multipleprefix“micro”means（）. A: thousandth(10tothe-3rdpower) B: millionth(10tothe-6thpower) C: billionth(10tothe-9thpower) D: trillionth(10tothe-12thpower)

Of the sun’ s total output of radiant energy, the earth receives （） A: one tenth B: one millionth C: all that comes from the surface of the sun D: a very small portion