Sunk costs are costs that cannot be changed by any decision now or in the future because of past decisions. Sunk costs should not affect our decisions from a rational perspective. However, we often want to recover or Avoid sunk costs and make a lot of irrational decision-making actions. It is called the sunk cost effect. According to the above definition, which of the following are not sunk cost effects? ['Xiaoming lent 10,000 yuan to a friend a year ago. But his friend was unable to repay because of bankruptcy. So he decided not to.', 'Xiao Zhao believes that he has been with his girlfriend for 8 years. He has put in so much time and energy. So he decided not to break up.', 'Xiao Wang spent 20 yuan to buy a bottle of soda. I found it difficult to drink. I wanted to throw it away. But considering that it was so expensive and I could n’t afford it, I had to drink it.', 'My mother bought an electronic keyboard for 2,000 yuan. But the child was not interested at all. So the mother decided to ask a tutor for 500 yuan per month. The reason was: "Otherwise this piano would be wasted!".']