(Q).
Q: What element is an essential part of many molecules needed by living organisms? Choices: - helium - silicon - hydrogen - nitrogen A:
(A).
nitrogen

(Q).
Q: What layer high in the atmosphere protects living things from most of the sun's harmful uv rays? Choices: - Mesosphere - troposphere - stratosphere - ozone layer A:
(A).
ozone layer

(Q).
Q: What are waves that pass a fixed point in a given amount of time called? Choices: - tendency frequency - combination frequency - radio frequency - wave frequency A:
(A).
wave frequency