根据短文和首字母填空（每题0.5分，共5分）
Bill and Simon were good friends. One summer they were on h___1____.They wanted to sail around the Caribbean Sea in their boat for two weeks. During their trip, they saw many whales. Bill and Simon were very e__2___ because they wanted to see them very much. Unluckily, w_3____ they were watching them, the whales began to hit the side of the boat.
Suddenly, w___4__ started coming in, and they realized that they were in trouble. They q__5___ jumped into the lifeboat before the boat sank(沉没), and watched it disappear under the sea.
Luckily, they had enough food and water for about twenty d__6____. They also had a fishing line and a machine which could change sea water i___7__ drinking water. These two things helped them to survive during their terrible experience.
For the next fifty days they caught about ten fish a day and a__8___ them. They saw about twenty ships, but although they waved and shouted when the ships were passing , n__9___ saw them. They were becoming weaker and weaker. Then just as they were beginning to l___10___ hope,a fishing boat saved them.
单手持红绿旗上举，该指挥的旗语信号表示的意思是（）。