Can 1) 表示能力(体力、知识、技能)。 Can you lift this heavy box?(体力) Mary can speak three languages.(知识) Can you skate?(技能) 此时可用be able to代替。Can只有一般现在时和一般过去式;而be able to则有更多的时态。 I’ll not be able to come this afternoon. 当表示“经过努力才得以做成功某事”时应用be able to,不能用Can。如: He was able to go to the party yesterday evening in spite of the heavy rain. 2) 表示请求和允许。 -----Can I go now? ----- Yes, you can. / No, you can’t.
①表示能力 “能,会” eg: He can speak a little Japanese. ②表示请求或许可 “可以”,用于各种人称 eg: Can I help you? ③在肯定句表理论的推测,不涉及某事是否会发生 ,关键词sometimes e.g. It is usually warm in my hometown in March, but it can be rather cold sometimes.