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一、选择题(一)单项选择题某山区中学的地理兴趣小组,利用课余时间进行野外考察。该地理兴趣小组利用测物体的日影的长度和方位(如图1,用北京时间)及北极星的仰角来确定当地的位置(如图2),同时,发现某山南北两翼的山麓地带沉积岩质地较疏松,而山顶同类沉积岩则较坚硬,但时间上山麓岩石早于山顶。在山麓地带沿河谷底部采集沉积物样本,发现从西北向东南,沉积物依次以粉沙、砂、砾石为主。据此回答1～3题。
I. Multiple-choice questions (1) Single-choice questions The geographic interest group of a mountain school in middle school will use field time to conduct field trips. The geographic interest group used the length and azimuth of the measured object’s sun shadow (Figure 1, using Beijing time) and the elevation angle of the Polaris to determine the local location (Figure 2). At the same time, it discovered the sedimentary rock texture of the foothills of the north and south sides of a certain mountain. It is relatively loose, while the same kind of sedimentary rock on the top of the mountain is harder, but the rock on the mountain is earlier than the top of the mountain. Sediment samples were collected along the bottom of the valley in the foothills. It was found that the sediments were dominated by silt, sand, and gravel from northwest to southeast. Answer 1 to 3 questions accordingly.