While elephants born without tusks（长牙）are not unheard they normally form just 2 to 6 percent of the population.However,that is not the case at Mozambique's Gorongosa National Park,where an astonishing 33 percent of female elephants born after the country's conflict ended in 1992 are tuskless.While that may appear to be just a coincidence,Joyce Poole,an elephant behavior expert,has another theory.The researcher thinks we may be witnessing unnatural evolution of the species due to the constant hunting of elephants for valuable ivory.
Poole says before the country's 15-year-long conflict,the park was home to over 4，000 elephants.However,by the time the conflict ended in 1992，about 90 percent of them had been killed for ivory to get money.Of the less than 400 survivors,over 50 percent of adult females had no tusks.Therefore,it is not surprising that the park's tuskless elephant population has grown greatly.
This is not the first time researchers have observed a great change in the population of elephants.At Zambia's South Luangwa National Park and Luangwa Game Management Area,areas which were heavily hunted in the 1970s and 1980s,35% of elephants 25 years old or older and 13% of those younger than 25 are now without tusks.A 2008 study published in the African Journal of Ecology found that the number of tuskless females at the Ruaha National Park in Tanzania went from 10.5 percent in 1969 to almost 40 percent in 1989，largely due to illegal hunting for ivory.
The recent ban on ivory in both the US and China should help get rid or a least reduce,elephant hunting.However,scientists are not sure how long it will lake for elephants with a higher rate of tuskless females,to change the trend.



What is the probable cause of the phenomenon mentioned in Paragraph 1？ ______

A. Illegal hunting.
B. Constant fanning.
C. A pure coincidence.
D. Natural evolution.

Why did people kill so many elephants during the conflict in Mozambique？ ______

A. To get money by selling ivory.
B. To develop new decorations.
C. To provide food for local people.
D. To make ivory products.

Which of the following had the earliest record on tuskless elephants？ ______

A. Gorongosa National Park.
B. South Luangwa National Park.
C. Ruaha National Park.
D. Lupande Game Management Area.

What does the underlined phrase "the trend" in the last paragraph refer to？ ______

A. Elephants facing greater danger.
B. Elephants growing more slowly.
C. Fewer female elephants staying alive.
D. More female elephants being tuskless.