What is the answer to this?

Plsss helpp

Look at the figure above. which atmospheric layer has around 80 percent of the mass of the earth's atmosphere? (hint: it's where the clouds seen on earth are formed.) a. exosphere b. troposphere c. stratosphere d. thermosphere

Why do we perceive objects as retaining their brightness under different lighting levels?

Which number represents a basic ph, 4 or 9? numerical answers expected! answer for blank 1: i'll give