Because light travels in a straight line and casts a shadow, Isaac Newton hypothesized that light is

A. a stream of particles.
B. a wave.
C. heat.

stream of particles

To determine Isaac Newton's hypothesis regarding light, we can look into his work. Isaac Newton hypothesized that light is composed of particles. This hypothesis formed the basis of Newton's corpuscular theory of light, which suggested that light is made up of tiny particles that travel in straight lines and produce the phenomenon of reflection and refraction.