The population growth rate in Kerala is the lowest among major Indian states. Which one of the following is the most widely accepted reason for this?

1. (a)Kerala has made the highest investment in family planning
2. (b)Kerala has the highest literacy rate in India
3. (c)Kerala has invested heavily in promoting literacy and public health and placed high priority on social policies
4. (d)The population pyramid in Kerala has relatively fewer women in the reproductive age group