填空题 Complete the sentences below.Choose ONE WORD ONLY from the passage for each answer.Write your answers in boxes 34-36 on your answer sheet.

填空题 1dune is said to have long ridges that can extend hundreds of miles.

填空题 According to Bagnold, an 1is needed to stop the sand from moving before a dune can form.

填空题 Stephane Douady believes the singing of dunes is not a spiritual phenomenon, but purely 1.