Question

Because light travels in a straight line and casts a shadow, Isaac Newton hypothesized that light is
A. radiation.
B. a stream of particles.
C. a wave.
D. heat.

Answer 1

B. A stream of particles, or otherwise known as photons, small pieces of light. All of the rest of the options could never make a shadow. 

Answer 2

B. a stream of particles.

hope this helps