1.选 to catch,形式主语提上来,实际上去to a cold in winter or spring是主语.你也可以记作固定用法,it is +adj+for sb.to do sth.
2.to stay.to do sth.往往表目的.
3.选passing.stop doing sth,阻止做某事.stop to do sth.停止手上做的事去做另一个,依据题意应选passing.
4.are coughing,表示你现在正在得感冒.
5.keep.had better do sth.固定搭配.