单项选择题A.One hundred.B. Only one.C.Four hundred.
单项选择题A.By observing the oldest stars in the universe. B.By studying the nearest stars that can be seen. C.By fixing the age of the oldest stars in the Galaxy.
单项选择题A.15 million dollars.B.50 million dollars.C. 5 million dollars.
单项选择题A.One week.B.One month. C.Two daysD.Three days.
单项选择题A.EggsB.DietsC.ProteinD.Exercises