Reasons for population growth in the 21st century include increase cropland the green revolution and

a desertifaction
b urbanization
c improve health care
d seasonal changes

Tides are caused by a differences in the gravitational force of the sun at different points on earth. differences in the gravitational force of the moon at different points on earth differences in earth’s gravitational field strength at different points on earth’s surfac fluctuations in the gravitational attraction between earth and the moon.