You Are a Landscape Architect Working on the Grounds of a Large

You are a landscape architect working on the grounds of a large estate. After you plant a dozen trees, the owner says, "There's been a mistake. The flowers on some of these willow trees look totally different! I specifically asked for Salix alba. You must have planted two different species." You refer to your tree guide, and read: "Salix alba - species of willow native to Europe and Asia, noted for the white undersides of leaves. Insect pollinated, dioecious. Grows 10-30m tall." How do you respond to the client?

A) "Sorry about that sir, I will dig up the wrong trees right away."
B) "Don't worry, the trees with the smaller flowers just haven't undergone phase change yet."
C) "Don't worry, when the shorter trees reach full size, they will grow the other kind of flower."
D) "Don't worry, Salix alba is dioecious, meaning each tree has either male or female flowers. That is why they look different."