2.It"s no good/use/fun+doing sth. It"s no use talking to him again. It"s no good eating too much fat. 這裡it是形式主語，而真正的主語是動名詞，但如果加了執行者，應該用：It"s no good for you to eat too much fat.
3.It
is dangerous climbing a tree. It is terrible not being allowed to smoke at all. It is nice helping other people. It is interesting planning a holiday. 但important,necessary,possible,impossible...等形容詞不能用上述結構，如 It"s important learning foreign languages.(×) It"s important to learn foreign languages.(√) 4.主語與表語必須一致。 Eg. To see is to belive.(√) Seeing is believing.(√)
應該是動名詞而不是現在分詞做主語，而動名詞做主語和不定式做主語區別主要有以下幾點：
1.不定式作主語經常表具體的動作，常與特定的連用(具體)，而動名詞作主語經常表示抽象的動作，一般不與特定的執行者連用(抽象)。
2.It"s no good/use/fun+doing sth. It"s no use talking to him again. It"s no good eating too much fat. 這裡it是形式主語，而真正的主語是動名詞，但如果加了執行者，應該用：It"s no good for you to eat too much fat.
3.It
is dangerous climbing a tree. It is terrible not being allowed to smoke at all. It is nice helping other people. It is interesting planning a holiday. 但important,necessary,possible,impossible...等形容詞不能用上述結構，如 It"s important learning foreign languages.(×) It"s important to learn foreign languages.(√) 4.主語與表語必須一致。 Eg. To see is to belive.(√) Seeing is believing.(√)