It’s difficult to get ahead but ______(要保持领先就更难).

A. never
B. ever
C. often
D. seldom

A. Glaciers are diversified in shapes and sizes.
B. Glaciers can be divided into valley glaciers and ice sheets.
C. Glaciers are remnants of great shrouds of ice that covered the earth years ago.
D. Few glaciers have a long history.