单项选择题
A.over the past 50 years B.beneath the earth’s surface C.by more than 50 percent D.for more than four decades E.as a raw material F.for home energy needs
A.in spite of B.because of C.as a result of D.such as
A.How the Big Bang occurred about 13 billion years ago. B.How“cosmic dark ages”came into existence. C.How dust grains and gases were formed after the Big Bang. D.How the first stars came into being after the Big Bang.