Which of the above are the inputs to MRP systems?

Question

Consider the following          

1. A mass production schedule

2. An inventory status file

3. Bill of material

Which of the above are the inputs to MRP systems?

(a) 1, 2 and 3                  (b) 1 and 2 only

(c) 2 and 3 only              (d) 1 and 3 only