了如指掌还是了如指掌 “了如指掌”v.s“一无所知”

1. to know/learn something by heart 记住;背诵
I can recite this poem without looking at it. I know it by heart.
我不用看就能把这首诗背出来 。我已经把它背下来了 。
2. to know something like the back of one’s back 了如指掌
He's lived in this city all his life. He knows it like the back of his hand.
他在这座城市住了一辈子,对这里可以说是了如指掌 。
3. know something inside out 了解彻底
She spent twenty years studying the history of London. She knows it inside out.
她学了20年的伦敦历史 。对此,她已经了解的十分彻底了 。
4. know next to nothing 几乎不了解;几乎一无所知
I'm really not interested in politics. I know next to nothing about it.
我对政治实在没什么兴趣,对此几乎一无所知 。
5 .not have the faintest idea 一点都不知道
'Which is the longest river in the world?' 'I haven't the faintest idea.'
“世界上最长的河流是哪条河?”“我没什么概念 。”
6. haven’t got a clue 一点不知道
'Can you tell me where Portsmouth Road is?' 'Sorry, I haven't got a clue.
“你知道朴次茅斯路怎么走吗?”“抱歉,我不知道 。”

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