单项选择题 After you enter Thimble Shoal Channel，you will alter course to pass between Trestle “A” and “B”. Which channel should you use?（）

单项选择题 After you enter the Ohio River at Cairo，which span of the Illinois Central RR Bridge would you select to pass under? （）

单项选择题 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? （）