返回派生类型时“未实现接口”

The following code:

以下代码:

public interface ISomeData
{
    IEnumerable<string> Data { get; }
}

public class MyData : ISomeData
{
    private List<string> m_MyData = new List<string>();
    public List<string> Data { get { return m_MyData; } }
}
public interface