[D] To follow the track of the Soviet warships under water.

　　65. What was special in their recorded sounds?

　　[A] A strange, powerful animal sound was heard. [C] A sea monster's sound was heard.

　　[B] A big whale's sound was heard. [D] A giant squid's sound was heard.

　　66. What can be concluded from the passage?

　　[A] Scientists' discoveries always change people's belief.

　　[B] There are too many secrets to be discovered.

　　[C] Megalodon may be still alive deep in the ocean.

　　[D] "Deep sound channel" allows sound waves to travel undisturbed.