Final answer:
Two-wheelers are exempt from NHAI Fastag tolls as Fastag is currently not applicable to them. Electric and commercial vehicles are not exempt simply based on their type. All vehicles is incorrect as most four-wheeled vehicles require a Fastag.
Step-by-step explanation:
The vehicles that are exempted from NHAI Fastag tolls include certain special categories like emergency vehicles, but as for the options provided:
- Two-wheelers are inherently exempt from Fastag tolls as the system is currently not applicable to two-wheelers.
- Electric vehicles are not generally exempted from Fastag tolls solely because they are electric.
- Commercial vehicles must use Fastag for toll payment unless they fall within an exempted category.
- All vehicles is incorrect since the majority of four-wheeled vehicles are required to use Fastag.
So, the correct answer is a. Two-wheelers.