Which of the following will fail to check the problem of the population explosion?

Government has taken various measures to check the increasing population

1.  To motivate smaller families to use various contraceptive methods (most important step).
2.  Many couples have adopted an 'one child norm'.
3.  Marriageable age of the female is increased to 18 years and that of males is increased to 21 years.
4.  Incentives are given to the couples with small families.