科学家们正在研究深海潜艇以探索海洋奥秘。

Scientists are studying deep-sea ___submarines to explore ocean mysteries.

我们点了两个金枪鱼潜艇三明治当晚餐。

We got two tuna ___subs for dinner.

海豚经常潜到水下寻找食物。

Dolphins often ___submerge to search for food underwater.