Final answer:
A. 0.04. In the US, the legal BAC limit for operating a commercial motor vehicle is 0.04%, compared to 0.08% for driving a regular passenger vehicle. Drivers under the age of 21 are prohibited from having a BAC level of 0.01% or more.
Step-by-step explanation:
In the US, it is illegal to operate a commercial motor vehicle with a blood alcohol concentration (BAC) level of 0.04% or more by weight of alcohol in the blood.
The legal limit for driving a regular passenger vehicle is 0.08% BAC.
A BAC level of 0.01% or more is not allowed for drivers under the age of 21, as it is considered illegal regardless of the vehicle type.