Awave front has the form of a
a. sine wave.
b. straight line.
c. circle.
d. surface of a sphere.

The rigth answer is D.

The wavefront or wavefront is an equal phase surface of a wave, i.e., these points have the same travel time from the source. The concept is used to describe the propagation of waves such as sound or electromagnetic radiation (light, radio waves, etc.). In a homogeneous and isotropic medium, in which the waves propagate without deformation, two types of particular waves are distinguished according to whether the wavefronts are spheres (spherical wave) or planes (plane wave).

one would be wind another would be water density

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.