单选题 Complete the sentences below using NO MORE THAN TWO WORDS from the passage.Write your answers in boxes 23-26 on your answer sheet.

填空题 It is a great mystery that young birds like cuckoos can find their wintering grounds without 1.

填空题 Evidence shows birds can tell directions like a 1by observing the sun and the stars.

填空题 One advantage for birds flying at night is that they can avoid contact with

填空题 Laboratory tests show that birds can detect weather without 1signs.