Concept:Dicotyledonous crops produce seeds that contain two cotyledons or seed leaves.Explanation:Zea mays (maize) is a monocotyledonous crop because it has only one seed leaf.Oryza sativa (rice) is also a monocotyledonous crop.Elaeis guineensis (oil palm) is another monocotyledonous crop.Vigna unguiculata (cowpea) belongs to the Fabaceae family and has two cotyledons.When its seed germinates, it produces two seed leaves.Hence, cowpea is the only dicotyledonous crop among the options.Answer:D. Vigna unguiculata