Penicillin is a drug that kills bacteria. Today, many bacteria are resistant to this drug. How does natural selection best explain this observation?
A. Penicillin causes some bacteria to mutate.
B. Some bacteria survive penicillin and reproduce.
C. Resistant bacteria cannot be attacked by penicillin
D. Resistant bacteria mutate more quickly than normal bacteria.

Asolid cylinder and a cylindrical shell have the same mass, same radius, and turn on frictionless, horizontal axles. the cylindrical shell has light-weight spokes connecting the shell to the axle. a rope is wrapped around each cylinder and tied to blocks of equal masses that are held the same height above the ground. both blocks are released simultaneously. the ropes do not slip. which block hits the ground first? or is it a tie?

Since the energy was not raising the temperature of the water during these segments, what was the energy used to do instead? your answer must include an explanation of what is happening to the molecules.

Which sentences describe point source pollution? in this type of pollution, the source of the pollution is single and easily identifiable. when runoff water from the melting of snow mixes with debris, it creates pollution. the runoff water, mixed with pollutants, reaches large areas with disastrous effects. alternatively, when a wastewater treatment plant releases harmful chemicals into a stream, the chemicals pollute the stream water because they are not treated for safety.