Explanation:

- Bluetooth technology is built for short-range wireless connectivity between devices.

- Option 1: Sending of files within the range of 10 km - Incorrect. Bluetooth typically operates up to about 10 meters, not kilometers.

- Option 2: Sending an e-mail - While Bluetooth can facilitate connections that allow email sending, this is not its primary purpose.

- Option 3: Wireless connection between various devices/equipments over short distances - Correct. Bluetooth is ideal for connecting devices like headsets, keyboards, and phones within close proximity.

- Option 4: Downloading of movies from Internet - Bluetooth is not suitable for downloading large files or streaming due to its limited range and bandwidth.