399亿元用科学计数法表示为[ ]
A.3.99×109元
B.3.99×1010元
C.3.99×1011元
D.3.99×108元
答案:B
-My aunt goes to climb Mount Gu every Sunday.
-Oh? But she _______ hate climbing mountains.[ ]
A.used to
B.use to
C.uses to
D.is used to
旋转阳极X线管功率比固定阳极X线管功率
A.大B.小C.相等D.近似E.难确定