A．affords a good incomeB．is challenging althoughC．is ha……

单项选择题Xers” is repeated several times to refer to ______.

单项选择题The survey has revealed that in the past 40 years the public faith in the American government has dropped by ______.

单项选择题Sagittarius A is ______.

单项选择题Were it not for the new telescope high in the Andes Mountains, researchers would not have argued that ______.

单项选择题It may be inferred from the passage that jets of gas ______.