填空题 Questions 1-6
Answer the questions below.
Choose NO MORE THAN THREE WORDS from the text for each answer.
Write your answers in boxes 1-6 on your answer sheet.

填空题 What kind of underwater device was used to investigate the ocean before submersible boats were invented?

填空题 What was the crewman of the first American-built submarine trying to do before his mission failed?

填空题 What gave the Nautilus the ability to remain submerged for a long time?

填空题 When was a submarine first used successfully to sink an enemy boat?

填空题 What new type of propulsion did the Holland use on top of the water?

填空题 For what reason was Diesel's fuel considered safer than Holland's?