✨ 最佳解答 ✨
It is no use crying over spilt milk .
この文の it は形式主語でcrying~が真主語です。
Crying over spilt milk is no use.
とも書けますが、英語は主語 (Crying over spilt milk) が長くなることを嫌うので、形式的に主語をIt と置いてます。
It was a truly awful sight watching the numberless little wooden houses catching fire one after another, and flaming up like so many match-boxes.
の It も形式主語で、真主語は
watching the numberless little wooden houses catching fire one after another, and flaming up like so many match-boxes.
の部分です。長い真主語を文頭に置くと
Watching the numberless little wooden houses catching fire one after another, and flaming up like so many match-boxes was a truly awful sight.
という文になります。これも、英語は長い主語を嫌うので、形式主語の It を文頭に使ってます。