Which of the following, if true, is the most likely explanation for the discrepancy described above? A. Ammonia can be bought in a grocery store, but concentrated iodine must be obtained from somewhat more restricted sources, such as chemical supply houses. B. Ammonium triiodide is only one of several powerful explosives that can be made from ammonia. C. Many terrorists have been more focused on acquiring weapons of mass destruction, such as nuclear or biological weapons, than on developing conventional chemical explosives. D. Airport security devices are typically calibrated to detect nitrogen compounds, such as ammonia and ammonium compounds. E. Although generally stable when wet, ammonium triiodide is unstable when dry and explodes at the slightest disturbance.