Booster fan generally used in . . . . . . . .

Booster fans in mining are typically used in the "return" or "return airway."

In underground mining operations, air is circulated to provide fresh air to the working faces where miners are actively mining. After the air has traveled through the workings, it becomes contaminated with dust, gases, and other pollutants. This used air is then directed back to the surface through the return airway.

Booster fans are installed in the return airway to assist in moving this used air efficiently back to the surface for processing and purification. These fans help maintain a safe and healthy working environment for miners by ensuring the proper ventilation of the underground workings.

So, the correct answer is Option B: Return. Booster fans are generally used in the return airway of underground mining operations.