假如第一处错误已纠正，则第二处错误在哪里？应如何改正？

张明敏时隔30年再登春晚，而演唱歌曲由《我的中国心》变为《我的中国梦》，一字之差，彰显鲜明的时代主题。下列对中国心与中国梦及其关系认识正确的有（    ）

①中国心是“位卑未敢忘忧国”，是爱国主义       ②实现中华民族的伟大复兴是我们的中国梦

③中国心为实现中国梦提供强大的精神动力     ④只要具备中国心，就能实现中国梦

修改病句。

①夏夜，常常坐在小院里观赏星空。

②你去劝劝他，过去的往事就不必再提了。

③通过老师和家长的帮助，逐步养成了良好的学习习惯。

④指南针、造纸、火药、印刷术是我国的四大发明之一。

如图所示，半径为 $\frac{5}{13}l$ 、质量为m的小球用两根不可伸长的轻绳a、b连接，两轻绳的另一端系在一根竖直杆的A、B两点上，A、B两点相距为l，当两轻绳伸直后，A、B两点到球心的距离均为l．当竖直杆以自己为轴匀速转动并达到稳定时（轻绳a、b与杆在同一竖直平面内）．求：

    Surfing the Internet for fun will make you a better employee, according to an Australian study.

    The University of Melbourne study shows that people who use the Internet for their own reasons at work are about 9 percent more productive(具有创造性的) than those who do not. Study author Brent Coker said, “Surfing the Internet at times helps increase workers' attention.”

    “People need to relax for a bit to get back their attention,” Coker said on the university's website. “Having a short break, such as a quick surfing of the Internet, helps the mind to rest itself, leading to a higher total Internet attention for a day's work, and as a result, increases productivity (生产效率),” he said.

    According to the study of 300 workers, 70 percent of people who use the Internet at work surf the Internet for their own reasons during office hours. Among the most popular surfing activities are searching for information about products, reading online news, playing online games and watching videos. “Firms spend a lot of money on software to block their workers from watching videos, using social networking sites or shopping online,” said Coker. “That's not always a good idea.”

    However, Coker said the study looked at people who surfed the Internet in moderation(适度), or were on the Internet for less than 20 percent of their total time in the office. “Those who spend too much time surfing the Internet will have a lower productivity than those without.” he said.