I2C.NET API for .NET 2.0 and .NET 4.0

There are two versions of the I2C.NET API: i2capi_dotnet_net20.dll and i2capi_dotnet_net40.dll. Which one should I use?
This depends on the used runtime environment. Applications using .NET 2.0, NET 3.0, or NET 3.5 should use the i2capi_dotnet_net20.dll. For .NET 4.0, NET 4.5, and .NET 4.6 you will need the i2capi_dotnet_net40.dll.