A student takes four samples of a white crystalline solid and places each in a well plate. On top of each sample, she carefully places 20 drops of clear mystery liquids A, B, C and D. Her results for each well are:

Liquid A: The solid dissolves quickly.
Liquid B: The solid appears unchanged.
Liquid C: A brownish colored liquid is produced.
Liquid D: Fizzing occurs and the well becomes warmer.

In which well does a PHYSICAL change occur?

A)
A


B)
B


C)
C


D)
D