A) When the light is blocked by an opaque object it casts shadow on the screen.
b) When the propagation of light will occur and it will be blocked by an opaque object then only shadows will be formed.
c) The fully shaded inner region of the shadow cast by an opaque object, especially area of the earth or the moon experiencing the total phase of the eclipse is called umbra.The penumbra is in which only a portion of light source is obscured by an occluding body.
(please draw the diagram by yourself)
d) It occurs when the moon passes between the sun and the earth, and the moon fully or partially blocks the sun