The "waterline" on the ship is also called "lifeline". For the safety of navigation, there are several horizontal lines on the hull of ocean-going ships to show that they are different.

① In winter, the seawater temperature decreases and the density increases; When the same ship sails in different seasons and different sea areas, the buoyancy remains unchanged, the seawater density is high, and the boiling water volume is small. (You can score if you answer this question reasonably) ② Indian Ocean Line. North Atlantic winter route.

Analysis of test questions: ① In winter, the temperature of seawater decreases and the density increases; The buoyancy of the same ship is unchanged when sailing in different seasons and different sea areas. According to Archimedes' principle, F floating = ρ liquid V discharging G, the density of seawater is high, and the discharged water is small. If the answer to this question is reasonable, you can score it. (2) As can be seen from the data in the table, the salinity of the North Atlantic is higher than that of the Indian Ocean, with higher density, smaller displacement and shallow draft, so the horizontal line 1 in Figure 7 represents the Indian Ocean line, and the horizontal line 2 represents the North Atlantic winter line.