clamp|clamped|clamping

我需要一个夹子来固定这些纸板。

I need a ___clamp to hold these cardboard sheets together.

狗紧紧咬住骨头不放。

The dog ___clamped the bone and refused to let go.

警方正在严厉打击非法停车行为。

The police are ___clamping down on illegal parking.