{{B}}quEstions 18 to 20 ArE BAsED on thE Following tAlk.{{/B}}

A、thE thrEAt oF poisonous DEsErt AnimAls AnD plAnts.
B、thE ExhAustion oF EnErgy rEsourCEs.
C、thE DEstruCtion oF oil wElls.
D、thE sprEAD oF thE BlACk powDEr From thE FArEs.