题目内容：
Directions：In this section，there is a short passage with 5 questions or incomplete statements．Read the passage carefully．Then answer the questions or complete the statements in the fewest possible words on Answer Sheet2． Questions are based on the following passage.
注意：此部分试题请在答题卡2上作答。
According to the author，what may be the possible carriers of bird flu?
参考答案：
答案解析：