尽管表面很平静，但房间里暗藏着一股不满的情绪。

Despite the calm surface, there was an ___undercurrent of dissatisfaction in the room.

划船时要小心水面下的暗流，它们可能比表面看起来更危险。

Be careful with the ___undercurrent while boating—it can be more dangerous than it appears on the surface.