请问 “Our trans-Atlantic alliance has at its core two principles that are central to this mission” 中 at 是什么用法

如题.

2017-03-09 提问者:kraysco

教师解答

尚未回答。

学生讨论

Jackchen0717:

If you know "at its core", which is an phrase, u would understand the whole sentence

2017-03-10

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