sing的名词到底是singing还是singer为什么

sing的名词到底是singing还是singer为什么 唱歌的英语单词是singing还是sing a song? We often hear him ______ in the classroom.A.sing B.singing C.to sing D.sung到底是选sing 还是singing呢 具体理由 They often hear Sally___(sing)this song.是sing还是singing?为什么大家给的答案不一样 In spring,we can hear birds -----(sing) in the trees应该是填sing 还是singing呐老师说是填singing的这是为什么呢? I heard him singing there改被动句是heard singing还是heard to sing she usually sing还是singing还是别的 she was heard singing song just now如果有确定的时间,如yesterday morning 是用heard to sing 还是heard singing moral是可数名词还是不可数名词?当名词的时候,为什么有时候加s,有时候不加?到底什么时候加啊? It must be Mary's.Mary‘s到底是名词还是形容词性的所有格?换成“她”该怎么填? sing 的名词是什么? 是We can dance and sing 还是 We can dancing and singing 你擅长谁唱歌吗 是are you good at sing还是good at singing let's sing an Englishi song同义句转换是这样的形式：（ ）（ ）singing an English song还有，我想借字典怎么说？ 可数名词以f为结尾的到底是ves还是s我看都有啊怎么区分啊? listen, the girl ___in the next room sings is singing sang sing ?但是答案is singing 是错误的。为什么？ adapt的名词形式到底是adaption还是adaptation? sing | sang | singing | to sing的区别是什么?Most of the yung pepole enjoy ___ pop songs.A:sing B:sang C:singing D:to sing打错了，是 young