大学英语：Learning a language is easy这句话中动名词短语learning a language作主语。

　　1. Learning a language is easy. 这句话中动名词短语learning a language作主语。

　　又如：Seeing is believing .

　　2.Most adults who are learning a second language would disagree with this statement.

　　试找出句子的主干：

　　此句中who are learning a second language 是定语从句，用来修饰most adults.

　　Would 的用法?

　　3.Hundred, thousand, million, billion 表确数时不用复数形式，表概数时加S

　　Eg: a hundred , three hundred , four million ,

　　Hundreds of…

　　Thousands of …

　　Millions of…

　　Billions of…