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Unit 2 Sailing the oceans Period 1 Warming Up，Prereading & Reading 时间：45分钟 Ⅰ.介、副词填空 1．The voyages of travellers before the 17th century show that they were not________the mercy________the sea even though they did not have modern navigational aids. 2．On a clear day especially during the summer the sailors could use the sun overhead________midday to navigate by. 3．There is a special cloud formation which indicates there is land close________. 4．An early method of measuring speed involved throwing a knotted rope tied________a log over the side of the ship. 5．The number of knots that were counted________a fixed period of time gave the speed of the ship in nautical miles per hour. 6．________this way the ship could set a straight course even in the middle of the ocean. 7．________， it was awkward to use as one of the points of reference was the moving ship itself. 8．As the ship rose and plunged in the waves, it was________difficult to be accurate with any reading. 9．It works________measuring the angle between two fixed objects outside the ship using two mirrors. 10．This gave the seamen the local time and allowed them to find their latitude________sea. 答案 1.at；of 2.in 3.by 4.to 5.during 6.In | 
