How do you choose the right preposition in front of "which"? For example: 1) When Defoe was nearly sixty years old he turned to fiction and wrote the greater work by which he is remembered. (why is "by") 2)It It is sometimes said that the next best thing to eating food is talking about food. If this is true, we need the vocabulary with which to do it! ( Which stand for what? I'm confused) How do you choose the right preposition in front of "which" when you are writing or speaking? I found that it's really hard for me to make my own sentence with it even if I understand when I'm reading.

War machine? What does it mean? This is the context: Is that your ideal, tell a lie ? How could I trust you ? According to this, do you really think that you deserve a second chance ? Well, you understand nothing about the Chinese women ! Nothing ! Then she left instantly the restaurant like a war machine. Why is "war machine"? Because she leave quickly or angrily? when would you use "war machine"? Could you give me some examples? Thanks!

"for one's sake", what dose it mean? Can you give me some examples and explain them? Thanks a lot.

Trees have sentimental value for us. Today I want to talk about trees. I don’t know if people in other countries have same view but in China trees have sentimental value for us. It’s like one morning you get up early, you draw back your curtains and open your window. Your room is filled with brilliant sunshine and the tree is out there, like an angel. The fresh green jump into your sight, which will expel the last day’s unpleasant things from your mind and light the whole new day. Besides, there are other deep meanings about trees, one of my teacher has told me that a lot of Chinese people have gone abroad in the past few decades, but you can hardly find their tombs in the foreign land because they came back to their motherland when they were dying and this phenomenon is called “叶落归根”，which literally means the fallen leaves should return to their roots but now it means one’s old bones to be buried in one’s hometown. As for me, trees do have sentimental value, I want to plant a baby tree by my place, because most of trees live longer than humans. I want make the tree still being alive when I die, because may be my family and my friends will remember the time they spent with me when they see the beautiful tree.

What does it mean "get beat up"? Eg:I coundn't get beat up all by myself. Does it mean other people hit me or I hit others? I'm really confused, can you help me?