used to reply completely or to emphasize something and show that there is no doubt about it

She certainly had a friend called Mark, but I don't know whether he was her boyfriend. 她确实有个朋友叫马克，不过我不知道他是不是她男友。

"This is rather a difficult question." "Yes, it's certainly not easy." “这实在是个难题。”“是呀，确实不容易。”

"Do you think more money should be given to education?" "Certainly!" “你认为应当给教育拨更多经费吗?”“当然啦！”

"Had you forgotten about our anniversary?" "Certainly not! I've reserved a table at Michel's restaurant for this evening." “你是不是把我们的结婚纪念日给忘了?”“当然没有！我已经在米歇尔餐厅预订了今晚的桌位。”

used when agreeing or disagreeing strongly to a request

"Could you lend me £10?" "Certainly." “你能借给我10英镑吗？”“当然可以。”

"Did you take any money out of my purse?" "Certainly not!" “你是不是从我钱包里拿钱了?”“绝对没有！”

very likely to happen

She will certainly win the election if the opinion polls are accurate. 如果民意调查准确无误，她定会赢得这场选举。