forward与backward后为什么有时会加上s

forward与backward后为什么有时会加上s backward or forward? 英语单词翻译forward-backward glasses forward ever,backward never!什么汉语意思 backward and forward和back and forth的区别 谜语：What time is the same spelling backward and forward 谜语:What time is the same spelling backward and forward? forward and backward Euler method 怎么翻译?!在线等 着急 冀教版四年级英语课件课题是lesson forward and backward 类似backward,upward,forward的!英语单词有什么? integrate backward or forward 的意思如题 Now Danny is walking backward.为什么“backward要加s what time is the same spelling backward and forward?什么时间正着念和倒着念都一样? What time is the same spelling backward and forward?(谜语） 谜语：What lettle stand for sea?What time is the same spelling backward and forward? What time is the same spelling backward and forward?谜底是什么? “What time is the same spelling backward and forward?”的中文意思bang “What time is the same spelling backward and forward?”的中文意思