Gas vans were used by Nazis, as they poisoned victims with gas from the van's exhaust. Such a deadly vehicle had a air-tight compartment, in which exhaust gas were emitted for killing victims while the engine was operating. Thus, the victims were killed by carbon monoxide from exhaust gases and suffocation. It is believed that the gas van was first used in the Soviet Union in the 1930's.
The answer is: A.
