to后面什么时候是动词原形,什么时候加ing答:当to作为动词不定式的标志时,后面加动词原形,作为介词的词性时,用v-ing的形式。这些动词后面接的to用动词原形:want, wish, hope, manage, pretend, decide, learn, agree, expect, demand, long, ask, care, choose, dare, fail, offer, plan, prepare, promise, refuse, desire, happen, ...