Is the BMW's external circulation A or M?

[Luke]

BMW's external circulation is A, while M is the forced internal circulation. Below is an introduction to the related content of internal and external circulation: 1. Internal circulation: When using internal circulation, the vehicle's interior space is like a sealed environment. Whether it's the cold or hot air blown out by the air conditioning, it circulates within the car, and no fresh air enters the vehicle. 2. External circulation: When external circulation is turned on, fresh external air flows into the car, improving the air quality inside the vehicle, which is also a good way to use it. Below are extended details on whether to use internal or external circulation during normal driving: 1. Summer: Turn on the internal circulation when using the air conditioning in summer to prevent outside heat from entering the car, during smoggy days, or when stuck in traffic to avoid outside air from entering the vehicle. 2. Highway: Use external circulation when driving on the highway to ensure fresh air circulation, when smoking to quickly expel smoke, or after the car has been exposed to the sun to release toxic gases from the interior.