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>

Which experts have real expertise? This video is sponsored by Brilliant. The first 200 people to sign up via ... ... <看更多>

每日一字：內行的能手形容對什麼在行，除了可以用be good at 之外，下次可以用be adept at / be proficient in / be expert at/on/in (He is not only good at ... ... <看更多>