n. a secret group organized to overthrow a government or occupation force
r. in or into hiding or secret operation
r. beneath the surface of the earth
n. 地下, 地铁, 地道, 秘密活动
a. 地下的, 秘密的
adv. 在地下, 秘密地
1. The subway runs underground through the city.
地铁在城市的地下运行。
2. We found an underground tunnel that was very old.
我们发现了一条非常古老的地下隧道。
3. Many animals live in underground burrows to stay safe.
许多动物生活在地下洞穴中以保持安全。