In very early human history, complex sanitation systems were not needed because settlements were usually very small, like the village shown below. however, as cities became larger and population densities increased, one major advancement was the development of which to channel wastewaters away from human populations more effectively than in the past.

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

Afamily is one another name for a group on the table of elements.

6what is the importance of water on earth? a) it keeps the top layer of the geosphere cool b) it allows life to exist c) it provides ice at the poles d) it creates earth's blue color from space