Your question is another cup of tea．

你的问题完全是另一回事。

　　another cup of tea，原意是“另一杯茶”，引申为“另一回事”。
例句：Even if you read French easily，you'll find it's another cup of tea to make conversation in French．
　　即使你觉得阅读法语不难，你也会发现用法语对话完全是另一回事。