南京大学自考本科法律专业怎么毕业？是先把要考的...

设函数f(x，y)=X2+Y2+xy+3，求f(x，y)的极值点与极值．

辩证唯物主义认为，运动和静止的关系属于( )

A.本质和现象的关系
B.内容和形式的关系
C.绝对和相对的关系
D.可能和现实的关系

To us it seems so natural to put up an umbrella to keep the water off when it rains．But actually the umbrella was not invented as protection against rain．Its first use was as a shade against the sun．
Nobody knows who first invented it,but the umbrella was used in very ancient times．Probably the first to use it were the Chinese,way back in the eleventh century B.C.
We know that the umbrella was used in ancient Egypt and Babylon as a sunshade．And there was a strange thing connected with its use:it became a symbol of honor and authority．In the Far East in ancient times,the umbrella was allowed to be used only by royalty or by those in high office.
In Europe,the Greeks were the first to use the umbrella as a sunshade．And the umbrella was in common use in ancient Greece．But it is believed that the first persons in Europe to use the umbrella as protection against the rain were the ancient Romans.
During the Middle Ages,the use of the umbrella practically disappeared．Then it appeared again in Italy in the late sixteenth century．And again it was considered a symbol of power and authority．By 1680,The umbrella appeared in France,and later on in England.
By the eighteenth century,the umbrella was used against rain throughout most of Europe．Umbrellas have not changed much in style during all this time,though they have become much lighter in weight．It wasn't until the twentieth century that women's umbrellas began to be made,in a whole variety of colors.

According to the passage,which of the following is NOT true?

A.Women enjoy using umbrellas with various kinds of colors nowaday
B.The inventor of the umbrella is unknow
C.Once ordinary people had no right to use umbrell
D.Umbrellas were popular and cheap in ancient time