Answer:
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast.
Explanation:
By clustering steel columns and beams in the skyscraper's core, engineers create a stiff backbone that can resist tremendous wind forces.
Answer:
I think its is answer B, a TV ad.
Explanation:
I could be wrong, but I know I'd be more likely to buy something that I can actually see being used rather than seeing a picture or just hearing about it.