The correct answer is: increase.
Family planning is essential for curbing the rapid increase in population. This is because family planning allows couples to have the number of children they want and can afford, which helps to control population growth.
Option A, spread, is incorrect because it does not accurately describe the problem of population growth. Population growth is not a problem of people spreading out over a larger area, but rather of there being too many people in a given area.
Option B, spurt, is incorrect because it suggests that population growth is a sudden event, when in fact it is a gradual process.
Option C, augment, is incorrect because it means to make something larger or greater, which is not the goal of family planning. The goal of family planning is to control population growth, not to increase it.