北通涿郡之渔商,南运江都之转输,其为利也博哉!这是古人称颂（    ）

下列关于说法错误的有（   ）
①民族区域自治制度是一项根本的政治制度②造福人民的经济制度是公有制为主体，多种所有制共存③我国正处于社会主义初级阶段④人民代表大会是我国根本政治制度⑤我国的主要矛盾是人民日益增长的物质文化需要同落后生产之间的矛盾⑥社会主义制度是我国根本制度（   ）

【案例探究】探究亚欧大陆气候类型分布特点，归纳影响气候空间分布的主要因素。

    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.

城市渠化是指将城市内河河道取直，硬化河堤、河底，改造岸坡为直立砌墙或混凝土墙，把天然河道变成人工明渠，如图所示。据此回答下列小题。