What type of blood is needed for the job?

Sometimes at school we are asked to give up our plan period to fill in for a teacher that is going to be absent. Last week I was asked to sub in our Ag Science class. Since I know absolutely nothing on the subject, the teacher had the students research two Ag jobs on the Internet. The students were to answer four questions, like income and required education. I decided to spice up the class so I told students there were five questions and one of them was to find "what blood type was required for the job." Not one student questioned me on that. Instead, they all looked for the answer. After a few minutes hands started to go up and students started telling me they looked everywhere but they could not find out what blood type was needed for the job. Needless, to say I didn't mind subbing so much that day.