單項選擇題Air circulation is caused or affected by（）.

A.the rotation of the earth on its axis
B.convection currents caused by differences in radiant heating between equatorial and polar regions
C.mountain ranges
D.All of the above


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1.單項選擇題Aids to navigation marking the intracoastal waterway can be identified by（）.

A.the letters ICW after the aid's number or letter
B.yellow stripes，squares，or triangles marked on them
C.white retroreflective material
D.the light characteristic and color for lighted aids

2.單項選擇題After you get underway，what is the first river gage you will pass? （）

A.Bayou Sara
B.Baton Rouge
C.Head of Passes
D.Red River Landing

3.單項選擇題After you enter Thimble Shoal Channel，you will alter course to pass between Trestle “A” and “B”. Which channel should you use?（）

A.Thimble Shoal Main Channel or the South Auxiliary Channel
B.Any of the channels but keep to the right hand side
C.The South Auxiliary Channel
D.Thimble Shoal Main Channel

4.單項選擇題After you enter the Ohio River at Cairo，which span of the Illinois Central RR Bridge would you select to pass under? （）

A.Any span is navigable
B.Northbank or Southbank
C.Southbank span only
D.Northbank span only

5.單項選擇題After you enter the Ohio River at Cairo，the Map shows that the deepest water under the Illinois Central RR Bridge would be found under which span? （）

A.Right Descending Bank span
B.Left Descending Bank span
C.Center span
D.Water is equal under all spans