groan、moan、sigh与sob这些名词（动词）均有“叹息声、叹息”之意。
groan : 侧重指因受到难忍受的精神负担或强烈的痛苦等而发出沉重的呻吟，也指显示强烈不满的叹息声。
- We could hear the groans of the wounded soldiers.
我们能听到伤兵们的呻吟声。 - He looked at the piles of dirty dishes and gave a groan of dismay.
他看着成堆的脏盘子，发出一声沮丧的叹息。 - to groan with pain/pleasure
痛苦地呻吟；高兴得直哼哼 - He lay on the floor groaning.
他躺在地板上呻吟。
moan语气比groan强，多指拉长的或连续的悲叹（声）或呻吟（声）。
- He moaned with pain before losing consciousness.
他痛苦地呻吟，随后就失去了知觉。 - "Let me die," he moaned.
“让我死吧。”他呻吟道。 - Thelma's always moaning (about something), and forgets how lucky she actually is.
特尔玛总爱抱怨，忘记了实际上她是多么地幸运。
sigh : 多指无意识地发出表示沮丧、悲痛、悔恨或厌倦等情绪的深沉叹息。
- She sighed deeply and sat down.
她深叹一口气，坐了下来。 - "I wish he was here," she sighed (= she said with a sigh).
“我希望他在这里，”她叹息道。 - He leaned back in his seat with a sigh.
他向后靠在座位上长出了一口气。
sob : 指抽噎声或呜咽声，或边说边哭。
- You're not going to help matters by lying there sobbing!
你躺在那里哭并不能解决问题！ - I could hear her sobs from the next room.
我听见隔壁传来她的抽泣声。
