问题补充：
The Great Wall winds its way from west to east, deserts, mountains and valleys, until at last it reaches the sea.
A. across; through; over
B. through; on; across
C. across; along; up
D. across; over; through
答案：
A. across; through; over
B. through; on; across
C. across; along; up
D. across; over; through
解析：长城蜿蜒东下，过荒漠、越丛岭、穿山峡。从表面经过：across. 翻越：over. 从里面穿过：through. 故答案为D.
