题目内容：

In the frozen continent of Antarctica scientists fear an alien invasion — not from outer space, but carried in people’s pockets and bags.

Seeds and plants accidentally brought to Antarctica by tourists and scientists may introduce alien plant species which could threaten the survival of native plants in the finely balanced ecosystem.

“The people that were carrying the most had lots and lots of seeds. They really were real threats,” said Dana Bergstrom, from the Australian Antarctic Division.

“When we take things in through hitchhiking（搭车旅行） then we get species which are competitive. The plants and animals there are not necessarily competitive, so we’d start losing various precious biodiversity（生物多样性） on the (Antarctic) continent”, Bergstrom told Reuters.

Amongst the alien species discovered were the Iceland Poppy, and Annual Winter Grass — all from cold climates and capable of growing in Antarctica.

The Antarctic Peninsula, where most tourists travel, is now considered a “hot spot” on the frozen continent and the warmer the climate, the easier for seeds to grow. “The peninsula(半岛) is warming at some of the greatest rates on the planet,” said Bergstrom.

The study, the first continent-wide assessment of invasive species in Antarctica, surveyed about 1,000 passengers during 2007-2008, the first year of the International Polar Year, an international effort to research the polar areas.

Bergstrom said the one alien seed that had gained a foothold is Annual Winter Grass. It is a strong weed in the sub-Antarctic and is on the Antarctic island of King George. It has also made its way to the tail part of the Antarctic continent.

1.What does the passage focus on?

A. The human influence on the native plants.

B. The development of native plants.

C. The discovery of new plants.

D. The promising future of tourism.

2.What is the effect of alien plant seeds to Antarctica?

A. They contribute to the biodiversity.

B. They lead to the warming up of Antarctica.

C. They make the native plants more competitive.

D. They break the balance of the natural environment of plants.

3.What can we learn from the passage?

A. The International Polar Year started in 2007.

B. Visitors to Antarctica are mainly scientists.

C. Visitors to Antarctica bring seeds on purpose.

D. Tall Fescue Velvet grass grows well in warm places.

4.What is the purpose of writing the passage?

A. To introduce the native environment of Antarctica.

B. To warn people of the danger of alien plant seeds to Antarctica.

C. To explain the relationship between plants and climate.

D. To give visitors some tips on how to explore Antarctica.