For information about present national boundaries, we’d better refer to an up-to-date map.

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A. practical
B. frequent
(答案→)C. reliable
D. beneficial
解析：考查形容词辨析。Practical实用的，frequent频繁的，reliable可靠的，beneficial获益的，句意：关于目前国家边界的可靠信息，我们最好查阅一下最新式的地图。故选C。