entirely强调一个整体的“完全”；
totally强调数量上的“完全”.
fully的程度最深,可翻译为完全地彻底地十分地
completely可翻译为十分,完全地
1. The army made a completely successful attack on the enemy capital.
军队攻击敌人首都的行动非常成功.
2. But they forget it completely.
但他们完全忘了这个事实.
3. It completely slipped my mind.
对此,我一点也记不起来了.
1. I don't fully understand his reasons for leaving.
我不完全理解他离开的理由
2. I fully agree with your views.
我完全同意你的观点.
3. I'm afraid he's fully engaged.
恐怕他会很忙.