Fans are used to circulate air in rooms and buildings and for cooling and drying people, materials, or products. Even though air that is circulated be a fan is comforting, no fan actually cools the air. Air conditioners use a complicated process to cool the air and create changes in temperature. While repairing a fan is relatively simple, a professional repairman will often have to intervene when home owners face problems with their air conditioning units.

The word to intervene in the passage is closest in meaning to

• to get involved
• to be interested in
• to learn about
• to be prepared