条件一 k可以被10整除 所以 2^k的尾数有可能是4，也有可能是6，也就是余数可能为4或6 不确定，不充分
条件二 k可以被4整除 所以2^k的尾数一定是6，也就是除以10后的余数一定为6.充分 所以选B
- 【OG18-P680-668题】In a review of 2,000 studies of human behavior that date back to the 1940s, two Swiss psychologists, declaring that since most of the studies had failed to control for such variables as social class and family size, none could be taken seriously.
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- The author of the passage would most likely agree with which of the following statements about the link between increased solar activity and certain seasonal weather changes on the Earth?
- The passage provides information to support which of the following statement about La Nina?
- Which of the following most accurately describes the organization of the passage?