Essential Part Q15

15. glacier

                  a. mountain

                  b. winter

                    c. prehistory

                    d. ice

Answer:  d

 A glacier is a large mass of ice and cannot exist without it. A glacier can move down a mountain, but it can also move across a valley or a plain, which rules out choice a. Glaciers exist in all seasons, which rules out choice b. There are many glaciers in the world today, which rules out choice c.