6 Reindeer in the Arctic may ...

Решение:

В тексте говорится: "Scientists are now warning that the entire ecosystem of the Arctic region may be threatened. Plants that grow in cold conditions will either grow further north or die out, which will endanger the land animals that eat them. Consequently, animals such as reindeer, caribou and muskoxen may starve if they can't find enough to eat." Это означает, что олени могут потерять свою кормовую базу.

Ответ: B lose their food supply.