题目

 Rock climbing is ___ great fun. You will get close to ____ nature and take adventures at the same time.    A. /; /                        B. a; /                 C. a; the                  D. /; the 答案：A地球上最大的生态系统叫做（ ）A、生物圈 B、大气圈 C、水圈 D、岩石圈