This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Forensic Medicine
All of the following statements regarding diatom are true, EXCEPT: 
Select and explain. 
A. Diatoms are aquatic unicellular plants, B. Diatoms have an extracellular coat composed of magnesium, C. Acid digestion technique is used to extract diatoms, D. Presence of diatoms in the femoral bone marrow is an indication of antemoem inhalation of water
B: Diatoms have an extracellular coat composed of magnesium
Answer: B: Diatoms have an extracellular coat composed of magnesium 
Explanation: Diatoms are microscopic unicellular or colonial algae. It has a cell wall which is strongly impregnated with silica and contain chlorophyll and diatomin, a brown pigment. Diatoms secrets a hard silicaceous outer box like skeleton called a frustulae. They are heat and acid resistant. Ref:The Essentials of Forensic Medicine and Toxicology By Dr K S Narayan Reddy, Pages 329-30