1、因为土壤中缺乏植物赖以生存的氮。在沙漠地区选试验点,通过精密仪器测量,在此基础上进行研究,发现沙漠地区长时间气温较高,土壤中的氮以气体形式不断挥发,而最终不能回到土壤中。
2、干旱地区种植田地,在保障了充分的水和肥料的前提下,土地的出产不高。
3、沙漠中土壤里的氮为何不可返回。作者采用总分的说明顺序,将干旱地区和气候温和地区进行比较来说明的。
4、采用生动的语言来说明。如“气势汹汹”和“肆无忌惮”两个成语,运用拟人的修辞手法,将沙漠人格化,表现土壤沙漠化的严重,警示人们保护环境。
It ______ ______ ______ the train will be late.
答案:is likely that
2. It is likely that the typhoon will sweep across the island.
The typhoon ______ ______ ______ ______ across the island.
答案:is likely to sweep
3. I think trying to stop the couple quarrelling will be of no use.
I think it's ______ ______ ______ to stop the couple quarrelling.
答案:no use trying
4. Every time I was in trouble, he had no hesitation in helping me.
Every time I was in trouble, he came to help me ______ ______.
答案:without hesitation
5. He never hesitates to help if I have any problem.
He always helps me ______ ______ if I have any problem.
答案:without hesitation
6. I crossed the street so as not to meet him, but he saw me and came running towards me.
I crossed the street to ______ ______ him, but he saw me and came running towards me.
答案:avoid seeing
7. It seems that the students in that class have all passed the qualified exam.
All of the students in that class ______ ______ ______ ______ the qualified exam.
答案:seem to have passed
8. It seems that the boys of the class are playing football on the playground.
The boys of the class ______ ______ ______ ______ football on the playground.
答案:seem to be playing
1..不能删去。(1分)大约是约数,表估计,而银杏树历史久远,无法准确计算,只能说个大概。用“大约”体现了说明文语言的准确性。(2分)
2.银杏古老悠久,(2分)与同时代生活的恐龙一样普遍。(2分
3.列数字、(1分)举例子(1分)。准确具体的说明了银杏树的确是长寿的树种。(2分)
4.有极为发达的根系;生长缓慢;需要的养分少;很少受到病害虫的侵害。(每点1分)
5.第一问:(3分)抵抗病虫害、抵御污染、具有观赏性。第二问:(2分)写出一种树名,符合该树的特点。
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