Hello, I'm 'The French',
The singular subject is the sentence four.
I think you can a little seach by youself, it is nor vey hard.
You need to find the subject (who make the action of the verb) and after if you don't understand one word you take the dictionnay, the Cambridge Dictionnaries Online on internet after you know the right answer.
I am very kind with you, but try before by yourself.
Have a nice day.