一.主语：
主语(subject) 是一个句子的主题( theme)， 是句子所述说的主体。它的位置一般在一句之首。可用作主语的有单词、短语、从句乃至句子。
1.名词作主语。 如：A tree has fallen across the road. (一棵树倒下横在路上。)
Little streams feed big rivers. ( 小河流入大江。)
2.代词用作主语。如：You’re not far wrong. (你差不多对了)。
He told a joke but it fell flat. (他说了个笑话，但没有引人发笑
3.数词用作主语。如：Three is enough. 三个就够了。
Four from seven leaves three. 7减4余3。
4.名词化的形容词用作主语。
The idle are forced to work. 懒汉被迫劳动。
Old and young marched side by side. 老少并肩而行。
5.副词用作主语。如：Now is the time. 现在是时候了。
Carefully does it. 小心就行。