When "sub" means an underwater boat, what word is it short for?
译句：当“sub”表示水下船只时，它是什么单词的缩写？（答案附在文末）
sub /sʌb/ n. 潜水艇，替补队员；vi. 代替
例句：
• The sub has 44 crew members aboard.
潜艇上有44名海军队员。
• So I've been working as a high-school sub.
所以我一直在当高中替补教师。
short for 是…的略称，简称
例句：
• Call me Jo—it's short for Joanna.
叫我乔好了—这是乔安娜的简称。
• E-sports is short for electronic sports.
E-sports是电子竞技的简称。
• submarine /ˌsʌbmə'rin/ n. 潜艇
例句：
• The submarine rose to the surface.
潜艇升到水面上来了。
• The submarine submerged to avoid enemy ships.
潜艇潜入水中以躲避敌船。
答案：submarine
