Explanation:

- The thermometer is a tool used to measure temperature.

- The most common form is made of a glass tube.

- It has a fine bore or narrow passage inside.

- One end of the bore is shaped into a bulb.

- The other end of the tube is completely sealed.

- Option 1: Brass - Metal that's typically used in construction, not suitable for thermometer tubes.

- Option 2: Glass - Traditional material for thermometers, clear and allows for easy reading.

- Option 3: Plastic - Not common for traditional thermometers as it's not heat-resistant.

- Option 4: Metal - Heat conductor, but not typically used for visible temperature readings.