When and why did people start living in cities?

Which amusement park ride utilizes periodic motion a.slide b.bumper cars c.giant swing d.roller coaster

Without stratospheric ozone, which of the following would most likely occur? i. smog over major cities would be greatly reduced. ii. farms would produce surplus crops because of increased photosynthesis. iii. uv radiation would damage phytoplankton and reduce populations of aquatic consumers. i only ii only iii only i and ii i and iii

Recycled water is best used for a) drinking b) bathing c) lawns d) dishes e) laundry