冬天上课教室门窗关闭较久后．不少同学会出现打“呵欠”的现象，是因为（ ） A．打

在某无色透明的酸性溶液中，能大量共存的离子组是

A．Na⁺、K⁺、SO₄^2－、HCO₃^－

B．Cu²⁺、K⁺、SO₄^2－、NO₃^－

C．Na⁺、K⁺、Cl^－、NO₃^－

D．Ag⁺、K⁺、SO₄^2－、Cl^－

我国中小学强调“双基”教育，“双基”指的是______。

大众传媒有（）

A、报纸

B、电视

C、广播

D、互联网

下列各项小，可以按照当地适用税额减半征收耕地占用税的是( )。

A．供电部门占用耕地新建变电站

B．农村居民占用耕地新建住宅

C．市政部门占用耕地新建自来水厂

D．国家机关占用耕地新建办公楼

David: Since attempting to preserve every species that is currently endangered is prohibitively expensive, the endangered species whose value to humanity is the greatest should be accorded the highest priority for preservation.
Karen: Such a policy would be unsound because it is impossible to predict the future value of a species, nor is it always possible to assess the present value of species whose contributions to humanity, though significant, are indirect.
Which of the following is the main point of Karen’s reply to David

A．Although it would be desirable to preserve all endangered species, doing so is not economically feasible.

B．Even if the value to humanity of a given species is known, that value should not be a factor in any decision on whether to expend effort to preserve that species.

C．Species whose contributions to humanity are direct should have a higher priority for preservation efforts than species whose contributions to humanity are only indirect.

D．Since the methods for deciding which species have the most value to humanity are imperfect, informed decisions cannot be made on the basis of the assessment of such value.

E．(E) The preservation of endangered species whose value to humanity can be reliably predicted is more important than the preservation of species whose value for humanity is unpredictable.