There is a syntax error in the "Avoid conditionals" Section

[esofar]

Error:

interface IAirplane
{
    // ...

    public double GetCruisingAltitude();
}

The correct grammar should be:

interface IAirplane
{
    // ...

    double GetCruisingAltitude();
}

[thangchung]

Thank you for your finding. I have fixed it 👍