challenge: What is one of the primary applications of a Brewster angle microscope?
  
  A. Determining the optimal conditions for Langmuir-Blodgett deposition
  B. Visualizing the formation of nanoparticles in solution
  C. Analyzing the chemical composition of adsorbate films
  D. Observing the structure of Langmuir monolayers in three dimensions
  Answer: 