问题
选择题
Life in London has so many _____-nightclubs，good restaurants and so on. [ ]
A. collections
B. instructions
C. attractions
D. expressions
答案
答案：C
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Life in London has so many _____-nightclubs，good restaurants and so on. [ ]
A. collections
B. instructions
C. attractions
D. expressions
答案：C
，可见轨道半径增大到2倍时，向心力减小到原来的
，可见轨道半径增大到2倍时，向心力减小到原来的