A student in Obu'pu Secondary School discovers that he simultaneously needs a pen, an exercise book, an eraser and a ruler, but that he can purchase only one of these items. What is the first thing he is expected to do?

• A.Check how much he has
• B.Find out which is the cheapest of the items
• C.Draw up a scale of preference
• D.Weigh the opportunity cost of each item against the other
• E.