搜题请搜索小程序“爱下问搜题”
问题 填空题
下列说法中：
①若α∈(0，
π
2
)，则sinα+cosα的值不可能是
2π
7

②若-
π
2
＜θ＜
π
2
，sinθ+cosθ=a，a∈（0，1），则tanθ的值不可能是-
π
3
；
③函数f（x）sinx（x∈R与函数f（x）=x（x∈R）的图象只有一个交点；
④函数f（x）=
2tan
x
2
1-tan2
x
2
的最小正周期是2π；
⑤不存在x∈(0，
π
2
)使得2x＞3sinx成立．
其中正确说法的序号是______（注：把你认为是正确的序号都填上）
答案

①若α∈(0，

π
2
)，则sinα+cosα=
2
sin(α+
π
4
)∈(1，
2
)，由于
2π
7
∉(1，
2
)，故①正确；

②若-

π
2
＜θ＜
π
2
，sinθ+cosθ=a=
2
sin(θ+
π
4
)∈（0，1），故θ∈(-
π
4
，0)，则tanθ∈（-∞，-1），故②正确；

③由于函数f（x）=sinx（x∈R与函数f（x）=x（x∈R）的图象只有一个交点（0，0），故③正确；

④由于函数f（x）=

2tan
x
2
1-tan2
x
2
=tanx，故④错误；

⑤当x→

π
2
时，得到2x→π，3sinx→3，故⑤不成立．

故答案为①②③

综合

    目前我国的自然环境面临着极大的危机，一方面以城市为中心，以大气、水体、固体废弃物、噪声为重点的环境污染仍在加剧；另一方面以水土流失、荒漠化、森林和草地资源减少、生物多样性减少为特征的生态破坏的范围在扩大，程度在加剧。下图为我国部分地区环境问题分布图，据此回答下列问题。

（1）A地区存在的主要环境问题是________________， 形成原因是________________________________

    ______________________________________________。

（2）B地区沙漠形成的自然原因是____________________________________________________；C地区荒

    漠化加快的人为原因有___________________________________________________________________。

（3）D地区出现酸雨的原因是______________________________________；简述酸雨的主要危害_______

    _________________________________________________________________________________________

    ___________________________________________________（答出三点即可）。
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单项选择题

It sounds like a science fiction, but researchers say it’s a scientific fact: Microscopic organisms dubbed "killer algae" are paralyzing fish with unknown toxins and then eating away at their flesh. They might be making people sick, too.
The name given to this single-cell organism, or dinoflagellate, is Pfiesteria piscimorte- literally, "fish killer. " It was discovered at North Carolina State University in 1988, but at the same time, few scientists believed in its existence, much less in its highly unusual predatory nature. But ongoing research has led to international acknowledgment of the phenomenon and, recently, research funding.
Seemingly prompted by an unknown substance secreted by fish, the aggressive creature swims into action. It sends neurotoxins into the water and air, paralyzing a fish’s nervous system, and causing it to gasp for air at the surface. Eventually the fish suffocates. The killer dinoflagellate then attaches itself to the fish and begins sucking away at its flesh. This macabre scenario may help solve several sea mysteries, such as why fishermen report seeing "fish walks" (fish trying to leave the water) and pools of dead fish with holes eaten through them.
Whether humans are affected by the dinoflagellate’s toxin remains to be seen. Researchers think it’s unlikely eating fresh fish are in danger, but anyone with frequent exposure to the creature could be in peril. Several researchers working with the algae have reported bouts of memory loss and disorientation.
To understand the killer algae further, scientists must fully characterize their toxin and determine what stimulates them to attack. They also need to know if the algae are hurting fish populations, and whether pollutants make them more likely to attack.

It is implied in the passage that ______.

A. many scientists had known dinoflagellate before 1988
B. there had been no such organisms before 1988
C. many scientists were in doubt about the nature of the organism in 1988
D. no scientists knew anything about the organism in 1988
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