A2 used to reply completely or to emphasize something and show that there is no doubt about it

中文解释

（用于肯定的答复或强调）当然，毫无疑问，确实，肯定 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。