鸟类呼吸时气体交换的场所是（ ）
A：气囊
B：气管
C：肺
D：肺和气囊
如图，已知海岛A到海岸公路BC的距离AB=50km，B，C间的距离为100km，从A到C必须先坐船到BC上的某一点D，航速为25km/h，再乘汽车到C，车速为50km/h，记∠BDA=θ
（1）试将由A到C所用的时间t表示为θ的函数t（θ）；
（2）问θ为多少时，由A到C所用的时间t最少？
Hello! I'm Dolly. ①I work at a hospital. ②I'm a nurse. My house is not far from the hospital. ③So I walk to work.④And my brother is a teacher.⑤He goes to work by car.
①____ ②____ ③____
④____ ⑤____
A. How does he go to work?
B. Where do you work?
C. What does your brother do?
D. How do you go to work?
E. What do you do?
神采____ ____然泪下 不知所____ ____肩接____
