题干
The Great Wall is very .
A：short and wide
B：long and very old
C：wide and very beautiful
答案(点此获取答案解析）
B
The Great Wall is very .
A：short and wide
B：long and very old
C：wide and very beautiful
，沿BE方向前进30m，至点C处测得
，再继续前进 
至D点，测得顶端A的仰角为 
，求 