皮皮学,免费搜题
登录
logo - 刷刷题
搜题
【简答题】
Economically, it makes good sense to protect the rich biological diversity we inherited from our forebears. "From morning coffee to evening nightcap," writes Myers, "We benefit in our daily lifestyles from the fellow species that share our One Earth home." Without knowing it, we utilize hundreds of products each day that owe their origins to wild animals and plants. Indeed our welfare is intimately tied up with the welfare of wildlife. The economic benefits of the wild resources are enormous. By some estimates, for example, half of all prescription and nonprescription drugs are made with chemicals that came from wild plants. The commercial value of these drugs is around $20 billion per year in the United States and about $40 billion worldwide. The US Department of Agriculture estimates that each year genes bred into commercial crops yield over $1 billion worth of food. Similar gains can be documented for other major agricultural nations. About half of the increased productivity in corn over the last 50 years has resulted from "genetic transfusions" from wild relatives of corn or from corn' s early ancestors grown now only in isolated regions. Plants and animals lost before they can be explored for possible benefits will diminish our opportunities to fight disease and increase productivity. A dozen regions located in the tropics and subtropics are the sources of virtually all commercially valuable plants and animals. They provide a reservoir of genetic material essential for the battle to fight disease, drought, and insects. Their loss would be a global tragedy with far-reaching effects on the food supply.
手机使用
分享
复制链接
新浪微博
分享QQ
微信扫一扫
微信内点击右上角“…”即可分享
反馈
参考答案:
举一反三
【单选题】对任意实数a,b,c,给出下列命题:①“a=b”是“ac=bc”的充要条件;②“a+5是无理数”是“a是无理数”的充要条件;③“a>b”是“a 2 >b 2 ”的充分条件;④“a<5”是“a<3”的必要条件.其中真命题的个数是(  )
A.
1
B.
2
C.
3
D.
4
【单选题】有下列说法: (1)a>b>0是a 2 >b 2 的充要条件; (2)a>b>0是 1 a < 1 b 的充要条件; (3)a>b>0是a 3 >b 3 的充要条件. 则其中正确的说法有(  )
A.
0个
B.
1 个
C.
2 个
D.
3 个
【简答题】对任意实数a,b,c,给出下列命题: ①“a=b”是“ac=bc”充要条件; ②“a+5是无理数”是“a是无理数”的充要条件 ③“a>b”是“a 2 >b 2 ”的充分条件; ④“a<5”是“a<3”的必要条件. 其中假命题的个数是______.
【单选题】对任意实数a,b,c,给出下列命题: ①“ ”是“ ”充要条件; ②“ 是无理数”是“a是无理数”的充要条件; ③“ ”是“ ”的充分条件; ④“ ”是“ ”的必要条件. 其中真命题的个数是(    ).
A.
1
B.
2
C.
3
D.
4
【单选题】有下列说法:(1)a>b>0是a 2 >b 2 的充要条件;(2)a>b>0是 的充要条件;(3)a>b>0是的a 3 >b 3 充要条件,则其中正确的说法有 [     ]
A.
0个
B.
1个
C.
2个
D.
3个
【简答题】对任意实数a,b,c,给出下列命题: ①“a=b”是“ac=bc”的充要条件; ②“a+5是无理数”是“a是无理数”的充要条件; ③“a>b”是“a 2 >b 2 ”的充分条件; ④“a<5”是“a<3”的必要条件. 其中真命题的题号是______.
【判断题】 时段降雨量可表示为瞬时降雨强度对时间的积分形式。
A.
正确
B.
错误
【简答题】下列四个命题中 ①“ ”是“函数 的最小正周期为 ”的充要条件; ②“ ”是“直线 与直线 相互垂直”的充要条件; ③ 函数 的最小值为 其中假命题的为 ( 将你认为是假命题的序号都填上)
【判断题】在仓储业务中,存货人要求提前取回仓储物时,保管人可以拒绝。
A.
正确
B.
错误
【判断题】保管人可以要求存货人提前提取货物( )
A.
正确
B.
错误
相关题目:
参考解析:
知识点:
题目纠错 0
发布
创建自己的小题库 - 刷刷题