主系表结构中，is单独作谓语。
He is from America.
She is nine years old.
Tony is a middle school stude.
My mother is a nurse.
My father is an engineer.
My grandfather is a lucky man.
以上句子都是is单独作谓语的例子。
下列句子中的is作为助动词，和后面的分词一起构成谓语。
He is learning English now.
the apple is eaten by my brother.
is是系动词，只能构成主系表结构，不能作谓语。
读音：英 [ɪz] 美 [ɪz]
释义：是。
语法：be 的第三人称单数现在时形式，常放在其他词后缩写为 -’s。
例句：
Magda is now married to George Callerby and we are the best of friends.
