On the basis, the author raises the suitable basic level structure forms and types of highway road surface in the area.

在此基础上，提出了适合该地区的公路路面基层结构形式和基层类型。

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Both Delta and US Airways have a three-tier redemption structure, offering seats at the basic level, a midtier level at around 40, 000 miles for a domestic coach ticket and a full-fare level for as many as 60, 000 miles for domestic coach round trips.

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