Difference between 留神，留意，留心？ I am now learning 近义词 and got a problem with distinguishing the difference between  留神，留意，留心. The textbook says:


  他干什么特别留心，看书时也常常做笔记 （留神and留意arent allowed here）
  多亏我对他留了一点心，这个情况没有告诉他 （留神 and 留意 arent allowed here）
  你看得出来他吗？ 我没有留意 （留神 and 留心 arent allowed here） 


Why are some correct and some wrong?
You should understand the three characters in the words firstly.
心：Mind
意：Sense
神: Focus

So add 留(keep) before them, becomes:


留心：Keep in mind --> remember
留意：Keep in sensitive --> ?
留神：Keep on focus  --> look out / be careful


My translation may not accurate in English, if someone have better translation, please comment below.

In your example, 


sentence 1 talking about reading/studying, so 留心 should be the only correct word. 
Sentence 2, here 留心 is separated, it's a derivative usage in my opinion. It means "keep defensive (because I remember he did something bad.)". 
Sentence 3, I don't understand the meaning... and I don't want to guess (although I could) since it's a tutorial/exam, it should be clear.