Which of the Following Is a Major Step in the Process

Which of the following is a major step in the process of marketing a drug in the United States?
1) Isolation of the chemical
2) Identification of the chemical
3) Investigational new drug approval
4) New drug application

A) 1 only
B) 1 and 2 only
C) 1 and 3 only
D) 1,2,3,and 4