(B) changed

　　(C) accumulated

　　(D) needed

　　47. The world "it" in line 18 refers to

　　(A) sea ice

　　(B) salinity

　　(C) seawater

　　(D) manner

　　48. Why does the author mention the Weddell Sea?

　　(A) To show that this body of water has salinity variations

　　(B) To compare Antarctic waters with Arctic waters

　　(C) To give an example of increased salinity due to freezing

　　(D) To point out the location of deep waters

　　49. Which of the following is NOT a result of the formation of ocean ice?

　　(A) The salt remains in the water.

　　(B) The surrounding water sinks.

　　(C) Water salinity decreases.

　　(D) The water becomes denser.

　　50. What can be inferred about the water near the bottom of oceans?

　　(A) It is relatively warm.

　　(B) Its salinity is relatively high.

　　(C) It does not move.

　　(D) It evaporates quickly.