Why were mobile gas vans invented?
a. to provide a less painful and traumatic death for the victims
b. to make killing more impersonal for the nazi soldiers
c. to increase efficiency
d. to eliminate the handicapped
e. to kill jewish women and children

The correct answer is b. To make killing more impersonal for the Nazi soldiers.  These vehicles were developed when the most effective forms and methods for the mass murder of Jews were investigated. The exhaust gases were used to kill people by inhaling carbon monoxide by trailers or gas chambers called Gaswagen.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.