Plaque is the main enemy of healthy teeth.

牙菌斑是牙齿健康的首要敌人。

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The main force of the enemy met with a check.

敌人的主力受到了牵制。

《新英汉大辞典》

America promoted a strong dollar throughout the 1990s, when inflation was still thought to be the main enemy.

ECONOMIST: Currencies

He says that Russian people once again see the United States as the country's main enemy.

NPR: Rice, Gates Appeal to Moscow for Missile Defense