[单项选择]普通累犯是指判处有期徒刑以上刑罚的犯罪分子，刑罚执行完毕或赦免以后，在( )以内再犯应当判处有期徒刑以上刑罚之罪的犯罪人。
A. 三年
B. 四年
C. 五年
D. 十年

Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove in. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory. At least that is what is supposed to happen, but you can always question the competence of the person who carried out the observation.
In practice, what
A. a new hypothesis about gravity
B. careful measurements of Mercury’s motion
C. new practical considerations of Newton’s theory
D. newly predicted observations