A class of science students investigates and records short term effects of a tornado that destroyed an area near the school which change was not caused by the tornado a:trees were knocked down
b: species of squirrels became extinct
c: flooding damaged dam
d: Buildings were destroyed

the arctic is a region of the planet, north of the arctic circle, and includes the arctic ocean, greenland, baffin island, other smaller northern islands, and the far northern parts of europe, russia (siberia), alaska and canada.

3. dark matter

empty space could also be a simple vacuum