阅读短文，回答问题。（共5小题，每小题2分，满分10分）
Red squirrels used to be a common sight in British forests and countryside. But there are fewer than 140,000 red squirrels left now and most of them are in Scotland. However, grey squirrels (introduced from North America) are now so common that many people dislike them. They can be legally（合法的）trapped and destroyed.
On first sight, the two types of squirrel are similar. They both have a long tail, which helps the squirrel to balance when jumping from tree to tree, and the same large eyes, small ears and powerful back legs. However, the grey squirrel has a clear physical advantage over the red. The red squirrel has a head-and-body length of 19 to 23 centimeters, a tail length of 15 to 20 centimeters and a body weight of 250 to 340 grams. Compared to this, the grey squirrel is a larger animal. The head and body measures between 23 and 30 centimeters long and the tail is between 19 and 25 centimeters long. Adult grey squirrels are heavier, weighing between 400 and 600 grams. This size allows them to store more fat and helps them to survive a hard winter, which would be fatal（致命的）to their  smaller cousins .
So why are red squirrels losing out in competition with grey squirrels? Size is one factor, but there are others. Red squirrels live high up in trees, while grey squirrels spend more of their time on the ground. This means any loss of forests greatly influences the red squirrel population. Another reason for the grey squirrel’s success is its ability to use food provided by people. Like the fox, the grey squirrel can survive in towns and cities. The other problem for the red squirrel is disease. Both squirrels carry a certain virus. While this doesn’t seem to attack grey squirrels, it is fatal to red squirrels.

Which are introduced from North America, red squirrels or grey squirrels?
What helps the squirrel to balance when jumping from tree to tree?
How much do adult grey squirrels weigh at most?
Who are the “smaller cousins” mentioned in the second paragraph?
There are four reasons why red squirrels are losing out in competition with grey squirrels.
Please list TWO of them.（每条不得超过4个单词）