A

Blue whales, the earth's largest animals, call to  others of their kind, though exactly what these cries communicate remains a mystery. But these sounds have begun evolving  (Öð½¥Ñݱä). Since at least the 1960s, the pitch (Òô¸ß ) of Antarctic  blue whales has   downshifted. Scientists have theories as to why: all  involving humans.

The deepening of their sounds is not unique. Many  blue whales around the world have also dropped their pitch. In the study last year that analyzed more than 1 million individual recordings of whale calls, pitch shifts  were found across the species, and among populations(ÖÖȺ)that don’t necessarily interact with one another. This is to say, whatever has caused the change doesn't seem to have a specific geographic origin.

The underwater noises caused by ocean traffic and at­sea industries might seem likely criminals. However, scientists have identified lowered pitch even across populations of whales that live in seas without major shipping routes.

One possible explanation for the change is the achievements of global conservation efforts. As their populations grow, the whales may have decreased their volume because they are more likely to be communicating over short distances.

Last year's study of whale calls also suggests a threatening reason for the drop in pitch, however. Perhaps whales don't need to be so loud because sound waves travel farther in oceans made acidic by the absorption of carbon dioxide.

Carbon dioxide in the atmosphere, meanwhile, may also indirectly influence whale voices in other ways. A recent study shows that, during the summer, the whales must use their top volume to make themselves heard in the cracking ice—a natural sound increased by unnatural processes, as rising temperatures worsen ice­melt. So the impacts of a warming planet may modulate animal sounds even in remote places.

1£®To what extent does whales' pitch drop?

A£®Across the species.

B£®In the Antarctic Ocean.

C£®Among some populations.

D£®Within one million individual recordings.

2. What causes the evolving of whales' pitch according to the text?

A£®Less communication and more threat.

B£®Protection efforts and acidic sea water.

C£®Sharp decrease of whales' populations.

D£®Underwater noises by ships and industries.

3. What does the underlined word “modulate”  mean in the last paragraph?

A£®Produce.  B£®Damage.

C£®Balance.  D£®Change.

4£®What can we infer from the text?

A£®Man is the soul of nature.

B£®Man and nature are in one.

C£®Nature pardons no mistakes.

D£®Nature has the final say over man.