古代战争中，士兵们用大炮发射沉重的炮弹来摧毁城墙。

In ancient warfare, soldiers used cannons to fire heavy ___cannon-balls at city walls.

赛车像炮弹一样冲过终点线。

The race car shot across the finish line like a ___cannon-ball.

他跳入泳池时做了个完美的抱膝跳水动作，溅起大片水花。

He did a perfect ___cannon-ball dive into the pool, making a big splash.