They do seem interchangeable but to me "expert in" implies doing knowledge rather than knowing knowledge. So "expert in kung fu" is clearly ... ... <看更多>

Expert in/On /at কখন Expert in English কখন Expert on English কখন Expert at English আজকে কথা বলব Expert নিয়ে। ... <看更多>

... -accuse-weapons- expert - in -baldwin-case-of-drinking-smoking/ ... The weapons expert in the Alec Baldwin case was hungover on set, ... ... <看更多>