Answer: a. Check the car for mechanical problems
Step-by-step explanation:
Much like a house needs to be inspected before you move in, so also does a car. Especially when that car is an already-used car.
Regardless of how well the sellers may have made the car look aesthetically, Nasir should still have the car checked for mechanical problems as these are not visible upfront but can be very troublesome if present.
Checking the car would also enable him negotiate better because it would show the exact condition and he can take this into account during price negotiations.