Answer: a) Virtual School Gold Card
Step-by-step explanation: To compare the monthly interest rates of the three credit cards, we need to convert the annual and quarterly rates to monthly rates.
For Canadian Express, the monthly interest rate is 19.9% / 12 = 1.6583%.
For Virtual School Gold Card, the monthly interest rate is 1.67%.
For Bank of Brennan Super Credit Card, the monthly interest rate is (4.99% / 4) = 1.2475%.
Therefore, the Virtual School Gold Card offers the lowest monthly interest rate at 1.67%.