Task 1
Directions: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 through 40. For each question or statement there are 4 choices marked A, B, C, and D. You should make the correct choice.
Why don't birds get lost on their long flights from one place to another？ Scientists have puzzled over this question for many years. Now they're beginning to fill in the blanks.
Not long ago, experiments showed that birds rely on the sun to guide th
The reason why birds don't get lost on long flights ______.

A. have been known to scientists for years
B. have only recently been discovered
C. are known by everyone
D. will probably remain a mystery