Tornadoes require which of the following conditions?
a. Warm, dry air from the Rocky Mountains, cold, wet air from the Gulf of Mexico, warm polar air from the jet stream
b. A warm, humid, low pressure system, a cold, dry air mass, and a fast, high altitude air current
c. A warm, humid, low pressure system, a cold, dry air mass, and a slow, high altitude air current
d. A cold, humid, low pressure system, a dry, warm air mass, and a fast, high altitude air current