A：https://blog.nowcoder.net/n/8a2b3713f63f472589eabf4d3e441166 C：https://blog.nowcoder.net/n/64b04519f06b462b9735c9ed2dc8d7b6 D：https://blog.nowcoder.net/n/1ec9dc14110340859da098dcb00a3028