to keep

'to keep at' something means to continue doing something even if it is hard or unpleasant.

• Learning phrasal verbs is hard so you have to keep at it every day.
  
• I had to finish so I kept at it for an hour before I took a break.
  

'to keep back' means to not use or give away all of something.

• Keep back some of the cream to put on top of the dessert.
  
• We kept back some of the money for emergencies.
  

'to keep down' means to stop the number or level of something from rising.

• If we want to make a profit this year, we have to keep costs down as much as possible.
  
• I try to eat well and exercise regularly to keep my weight down.
  

'to keep off' = means to not go onto an area.

• Please keep off the grass.
  
• Keep off the motorway in the morning, there are always traffic jams at that time.
  

'to keep off' can also mean to not talk about a particular subject.

• He started talking about it. I tried to keep off the subject.
  
• He can't keep off the question of climate change, he never stops talking about.
  

'to keep on' means to continue with something.

• All night long he kept on asking me questions about it.
  
• I asked him to stop but he just kept on.
  

'to keep out of' means to not get involved in something.

• It's not my business. I keep out of their arguments.
  
• It's got nothing to do with me. I'm keeping out of it.
  

'to keep to' means stay on a subject when talking.

• We don't have much time so can we keep to the agenda, please?
  
• Can you keep to the point, please?
  

'to keep up' means to go at the same speed as someone or something.

• She was walking so fast that I couldn't keep up with her.
  
• I've got too much to do at the moment. I can't keep up with my work.
  

exercise1

exercise 2
exercise 3 to keep