Which of the following is true about natural selection?
a. natural selection usually causes a species to change suddenly.
b. natural selection does not cause a species to change.
c. natural selection is the only cause of changes in a species.
d. natural selection usually causes a species to change gradually. i beg me 18 points if you

Natural selection is a one of the basic mechanisms of evolution by which species adapt to their environment in order to increase their chance of survival and reproduction. It is the change in the characteristics that lead to survival. In natural selection, genotype variations that will increase the chance of survival and reproduction of some organism are preserved and will be inherited. So, natural selection will "select" those genotypes that help survival causing gradual change of species.

when the displaced particles are perpendicular to the direction the wave travels, is called a transverse wave, whereas in longitudinal wave the displace practices are parallel to the direction of the wave.

in the given image:

first image shows - longitudinal wave

second image shows - transverse wave

third image shows - longitudinal wave

fourth image shows - longitudinal wave