The text boxes in the left panel have been placed in a random order. Restore the original order by dragging the text boxes from the left panel to the right panel.
a) Traditionally, the black keys were made from ebony and the white keys were covered with strips of ivory, but since ivory-yielding species are now endangered and protected by treaty, plastics are now almost exclusively used.
b) Piano keys are generally made of spruce or basswood, for lightness.
c) Spruce is normally used in high-quality pianos.
d) Also, ivory tends to chip more easily than plastic.