Which of the following has the maximum osmotic at temperature T?

Question

$\begin{array}{1 1}(a)\;\text{50ml of 1M urea solution}\\(b)\;\text{100ml of 1M glucose solution}\\(c)\;\text{mixture of 50ml of 1M urea solution and 100ml of 1M glucose solution}\\(d)\;\text{all are isotonic}\end{array}$