All citizens are eager to strengthen urban greening, but when citizens are required to pay for a greening plan, there are always people who think that they can enjoy the benefits of greening even if they don't pay, so they refuse to bear the cost. Which of the following, if true, is the prerequisite for the above argument? ['These people like to take advantage.', 'These people think that greening should be funded by the government.', 'Money for green options is mandatory.', 'These people think that someone will always pay.']