Which of the following is a primary source?

a) an interview with an eye-witness

b) a biography of a celebrity

c) a u. s. history textbook

d) an article written about an event from the 1800s

I feel like A is the correct answer. Its from a witness of it. Articles written on it have been wrote and edited by many different people. If that makes any sense to you. 

Show his work so he doesn’t get points taken off. this is because even if he can do calculations in his head, he may make a mistake and having it on the paper will not only him find mistakes but show that he was doing the work as well.