What are the basic units of a chemical elements called ?

What class of levers is shown in this image?

When it is summer at the south pole, a. the northern hemisphere is tilted toward the sun. b. the southern hemisphere is tilted away from the sun. c. the northern hemisphere is tilted away from the sun. d. both the southern and northern hemispheres are tilted toward the sun.

Afive-year study was carried out on a population of algae in a lake. the study found that the algae population was steadily decreasing in size. over the five-year period this decrease most likely led to