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).
Answer : Option A) He asked what would happen if he deliberately inoculated someone with cowpox fluid from another person.
Explanation : Edward Jenner wanted to know what would happen if he deliberately inoculate the cowpox fluid from some person to another. He tested this experimental results and later on came up with the hypothesis. Which roughly state that someone will not get smallpox because they already had cowpox.
