Rule: Aircraft may only enter sector Alpha if: (1) altitude is between FL200 and FL400, and (2) the aircraft is on an approved route. Aircraft X is at FL250 on an approved route. Aircraft Y is at FL180 on an approved route. Aircraft Z is at FL300 on a non-approved route. Which aircraft may enter sector Alpha?
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A
Aircraft X only
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B
Aircraft X and Y
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C
Aircraft X and Z
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D
Aircraft Y and Z