Many more species are expected to die out completely unless we do something to help.除非我们伸出援手,否则估计会有更多的物种行将灭绝。Environmental pressures encourage genes with certain mutations to persist and others to die out.环境的影响使发生了某些突变的基因存活下来,另一些则消亡了。It's a custom that is beginning to die out.这是一种正在消失的习俗。