Piggyback is a system of unitized multimodal land transport by（）.
A. road and sea
B. road and rail
C. road and air
D. rail and road
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（）is a document granted by the customs authorities which allows a vessel tostart unloading goods.
A. Entry Inwards
B. Entry Outwards
C. Outward Export Permit
D. Inward Permit
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