一批木材全部用来加工桌子可以做30张，全部用来加工床可以做15张。现在加工桌子、椅子和床各2张，恰好用去全部木材的。剩下的木材全部用来做椅子，还可以做（）把。

A．40

B．30

C．25

D．5

Conservationists have believed that by concentrating their preservation efforts on habitats rich in an easily surveyed group of species, such as birds, they would thereby be preserving areas rich in overall species diversity. This belief rests on a view that a geographical area rich in one group of species will also be rich in the other group’s characteristic of the entire regional climate zone.
Which of the following findings about widely scattered tracts 10 kilometers by 10 kilometers in a temperate climate zone would most seriously challenge the conservationists’ assumptions

A．The tracts show little damage from human intrusion and from pollution by human activities.

B．Where a certain group of species, such as birds, is abundant, there is also an abundance of the species, such as insects, on which that group of species feeds, or in the case of plants, of the land and water resources it requires.

C．The area of one of the tracts is generally large enough to contain a representative sample of the organisms in the region.

D．There is little overlap between the list of tracts that are rich in species of butterflies and the list of those that are rich in species of birds.

E．(E) The highest concentration of individuals of rare species is found where the general diversity of species is greatest.