增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词；

2）只允许修改10处，多者（从第11处起）不计分。

Dear Tom,

    I'm happy to get from your letter and knew you're coming to China.

    Among the two trips to the Yangtze River and Mount Tai, both are high recommended (推荐). Personally, I prefer the tour along the Yangtze, longest river and one of the mother river of Chinese civilization. You can learn a tot about the history of China and Chinese people. Moreover, the scenery along the river are amazing, with many well-know sightseeing spots. That's because I think the trip along the Yangtze will be a better choice.

    I hope your suggestion will be of some help and you'll have a good time in China.

Yours,

Li Hua

    On March 14, maths and science lovers around the world celebrated a special day: Pi Day.

    Pi is____ to3. 14, but the number goes on endlessly. It is sometimes written in Greek,π. With the help of computers, mathematicians have been able to ____ pi out to over trillion (万亿) decimal places, but there is still no____ to the number. This makes pi puzzling, even for the most famous scientists and mathematicians.

    Pi Day is celebrated around the world on March 14, since how we write this date, 3/14,looks just like the number pi.

    For some people, the appeal (吸引力) of Pi Day goes far beyond maths and science. Pi shows up____popular culture. You can see it in movies, comics, music and more. "In modern movies, any time the filmmaker wants to evoke (产生) a sense of mystery, often the symbol pi is used, "says David Blatner, Jewish American writer of The Joy of Pi.

在菱形ABCD中，对角线AC=4，E为CD的中点，则$\overrightarrow{AE}·\overrightarrow{AC}=$____