What was robert brown looking at through a microscope when he found evidence of the 1827 scientific concept named in his honor?

He was looking through a microscope at particles trapped in cavities inside pollen grains in water. The concept of Brownian motion is named after him. This is the random motion of particles suspended in a fluid, liquid or gas resulting from their collision with the fast-moving molecules. Here, the patterns of motion of the particles are typically alternations between random fluctuations in a particle's position inside a fluid sub-domain with a relocation to another sub-domain. Each relocation is followed by more fluctuations within the new closed volume. 

C) reflection (i also looked up the other choices just to make sure)