题目

（本小题满分6分）如图，某人在点A处测量树高，点A到树的距离AD为21米，将一长为2米的标杆BE在与点A相距3米的点B处垂直立于地面，此时，观察视线恰好经过标杆顶点E及树的顶点C，求此树CD的高． 答案：解：∵CD⊥AD，EB⊥AD，∴EB∥CD. ∴△ABE∽△ADC．    …………………………………………………2′∴．                …………………………………………………3′∵EB=2，AB=3，AD=21，∴．         …………………………………………………4′∴CD=14．           …………………… Tired of the noise, ______. A. he shut the door                      B. the door had been shut C. he had shut the door                D. the door was shut