be of +n.结构

一、当名词为抽象名词时，这种结构相当于be+adj.。

此类用法的名词有importance/use/help/value/harm/difficulty等。

Sports and games can be very valuable.→Sports and games can be of great value.

二、当名词为表颜色、形态、种类、价格时，of有时可省略。

这类词有color/age/size/shape/type/kind/way/weight/height/price等。

They are (of) the same age/an age.他们同龄。

三、当名词为表物质的名词时，这类结构相当于be made of或be built of，意思为“由某种材料制成或构成”。

This wall is of bricks.→This wall is built of bricks.

四、当名词为集合名词时，这种结构相当于belong to+n.，其中of表从属关系。

这类词有class/family/school/factory等。

We are of the same class.→We belong to the same class.

五、有时be of + n.表出身、组成，相当于be born in或be made up of。

Lincoln was of a poor family. →Lincoln was born in a poor family.

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