结成联盟往往是为了共同防御。

Leagues are commonly made for mutual defense.

《新英汉大辞典》

1954年美台签订了共同防御条约。

S. They signed The Mutual Defense Treaty in1954.

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1954年美台签订了共同防御条约。

S. They signed The Mutual Defense Treaty in1954.

youdao