If Coal Has More Energy Per Gram Than Nitroglycerin, Why

Multiple Choice

If coal has more energy per gram than nitroglycerin, why isn't its combustion considered an explosion?

A) Its lower explosion level (LEL) is too low for it to be considered a true explosion.
B) It requires too high an ignition temperature.
C) The rate is too slow.
D) The concentration is never high enough for an explosion.