Following text is for questions 39 to 42.An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, the salty ocean mixes with a freshwater river, resulting in brackish water. Brackish water is somewhat salty, but not as salty as the ocean. An estuary may also be called a bay, lagoon, sound, or slough. Water continually circulates into and out of an estuary. Tides create the largest flow of saltwater, while river mouths create the largest flow of freshwater. When dense, salty seawater flows into an estuary, it has an estuarine current. High tides can create estuarine currents. Saltwater is heavier than freshwater, so estuarine currents sink and move near the bottom of the estuary. When less-dense freshwater from a river flows into the estuary, it has an anti-estuarine current. Anti- estuarine currents are strongest near the surface of the water, Heated by the sun, anti-estuarine currents are much warmer than estuarine currents.

39. What does the text tell you about?
A. The salt water area.
B. The freshwater river.
C. The estuary.
D. The water circulation.

40. Why is there saltwater in the estuary? Because ..
A. water evaporate in midday
B. there is so much salt in the estuary
C. freshwater comes from the rain
D. it is situated next to the ocean

41. The river water usually circulates into... out of an estuary.
A. then
B. SO
C. but
D. and

42. What probably happens if fresh water meets salt water in the estuary
A. The fresh water will mix with the salt water
B. It will not gather bacause fresh water has different volume
C. The fresh water will be beaten by the salt water
D. They will exist although in the same place​