请给我think about,think over,think of,think up的详细辨意

1think over:If you think something over,you consider it carefully before making a decision。2think up:If you think something up,for example an idea or plan,you invent it using mental effort。3think of,If you think of,you make an effort to remember things that happened to you in the past。4think about,If you think about it means you think it carefully