Mr Black was walking in the forest（森林） He was scared when he heard a terrible noise. But he could not get out of the forest. His friends were waiting for him in a village outside the forest. They would give him a lot of money if he took a tiger to them, or they were going to laugh at him.
    Mr Black liked hunting(打猎). He usually killed some birds and animals. But a week ago, after he drank too much, he called himself a brave hunter. So his friends bet(打赌) him twenty thousand dollars if he could kill a tiger.
    Suddenly, he heard a little noise. He ran to a big tree,and climbed up it quickly.He didn't come down until he saw it was a farmer. He went close to him and asked, “Excuse me, sir.Are there any tigers in the forest?”
    “Yes,” said the farmer. “I saw a lot of tigers' tracks（足迹）about a kilometer north near here.”
“Good!”Mr Black said in a hurry. “Which way is to the south,then?”

在西北的河套平原、宁夏平原、河西走廊和天山山麓，人们利用河水和高山冰雪融水，发展了____ 农业；在青藏地区的藏南谷地、湟水谷地等海拔较低的地区分布着____ 农业．

地理—选修3：旅游地理

近年来，在旅游景区兴起旅游玻璃栈道，玻璃栈道都离不开高、险，伴着悬崖而生，除了体验险要之外，还有一个很重要的点就是美景。身处玻璃栈道上精彩刺激，视野开阔，风景优美，群山秀色，一览无余。

分析旅游区玻璃栈道兴起的原因。

法国史学家米西勒认为，14到16世纪欧洲封建社会末期是“人”和“世界”发现的时代，这两个发现的共同影响是（    ）

用反证法证明”若x，y都是正实数，且x+y＞2，则 $\frac{1+x}{y}$ ＜2或 $\frac{1+y}{x}$ ＜2中至少有一个成立“的第一步应假设（   ）