Answer:
Option B. It is unrealistic
Step-by-step explanation:
The reason is that the people have different likes which means we will never see 100 percent acceptance from the customers which might in the way of rejecting the offer of Gary. So the assumption that 50,000 cab drivers will purchase its product is truly optimistic which in other words is unrealistic assumption. So the option B is correct.
Option A is incorrect because the assumption is less qualitative as it doesn't relies on realistic assumption.
The cab drivers sales are relevant here but the sales assumption was unrealistic (Highly optimistic assumption) so the option C and D are incorrect.
Option E is also incorrect because the sales to cab drivers can be measure by initially directly selling 1000 cell phone to 1000 cab drivers which will give an actual idea of sales units expected, which means it is measurable.