单选题
Coincident with concerns about the accelerating loss
of species and habitats has been a growing appreciation of the importance of
biological diversity, the number of species in a particular ecosystem, to the
health of the Earth and human beings. Much has been written about the diversity
of terrestrial organisms, particularly the exceptionally rich life associated
with tropical rain-forest habitats. Relatively little has been said, however,
about diversity of life in the sea even though coral reef systems are comparable
to rain forests in terms of richness of life. An alien
exploring the Earth would probably give priority to the planet's dominant, most
distinctive feature—the ocean. Humans have a bias toward land that sometimes
gets in the way of truly examining global issues. Seen from far away, it is easy
to realize that landmasses occupy one-third of the Earth's surface. Given that
two-thirds of the Earth's surface is water and that marine life lives at all
levels of the ocean, the total three- dimensional living space of the ocean is
perhaps 100 times greater than that of land and contains more than 90 percent of
all life on Earth even though the ocean has fewer distinct species.
The fact that half of the known species are thought to inhabit the
world's rain forests does not seem surprising, considering the huge numbers of
insects that comprise the bulk of species. One scientist found many different
species of ants in just one tree from a rain forest. While every species is
different from every other species, their genetic makeup constrains them to be
insects and to share similar characteristics with 750 000 species of insects. If
basic, broad categories such as phyla and classes are given more emphasis than
differentiating between species, then the greatest diversity of life is
unquestionably the sea. Nearly every major type of plant and animal has some
representation there. To appreciate fully the diversity of
abundance of life in the sea, it helps to think small. Every spoonful of ocean
water contains life on the order of 100 to 100 000 bacterial cells plus assorted
microscopic plants and animals, including larva's or organisms ranging from
sponges and corals to starfish and clams and much more.
单选题
What is the main point of the passage?
A. Humans are destroying thousands of species.
B. There are thousands of insect species.
C. The sea is even richer in life than the rain forests.