The changes that occurred in Yellowstone National Park after all of its wolves were killed showed that wolves are
A. harmful to the ecosystem
B. a keystone species in the ecosystem
C. a producer in the ecosystem
D. the only predators in the ecosystem

The following image is of a diatom. it lives in water and gets food from photosynthesis. it is encased in a hard shell made of something similar to glass or sand . a diatom is a(n) because it has a) multi-celled organism; specialized parts. b) vertebrate; a skeleton. c) insect; an exoskeleton. d) single-called organism; only one cell.

When coal has reached it hardest, darkest form, it is called select one: 0 a. sub-bituminous b. lignite c. bituminous d. antrhacite next page

Which type of scientific statement is defined as a hypothesis or group of hypotheses that can be accepted as true based on the repeated experimentation with similar results