Prior to the attacks on september 11 what was the deadliest attack on us soil

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks.