未知题型 （ ）是中国革命史上划时代的事件，是中国旧民主主义革命到新民主主义革命的转折点。

单项选择题 These studies will yield valuable lemons ________.A) in which to save lives and protect propertyB) how to save lives and protect propertyC) in how to save lives and protect propertyD) about those to save lives and protect property

单项选择题 ________ exposure to dirty air can cause people suffer from some diseases.A) RaisedB) ProlongedC) ExpandedD) Enlarged