They are changed because of the environments changing
Answer:
D. Sound
Explanation:
Both А. water and B. fans doing the "wave" in a football stadium are both literal waves and are not examples of a compressional/longitudinal
Answer:
A keystone species is an organism that helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether. ... Any organism, from plants to fungi, may be a keystone species; they are not always the largest or most abundant species in an ecosystem.
The answer is A, a vaccine. This is why they are often given to children for prevention.
