This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Asphyxia, Subject name: Forensic Medicine
The outer covering of diagram is made of - 
Select and explain. 
A. Magnesium, B. Silica, C. Hydrocarbons, D. None
B: Silica
Answer: B: Silica 
Explanation: Reff: The synopsis of forensic medicine & Toxicology 28th edition pg: 195 Cell wall is usually strongly impregnated with silica and contain chlorophyll and diatoms a brown pigment. Diatom secretes hard siliceous outer box like skeleton called frustule. They resist heat and acid