Explanation:

- The thermometer is an instrument for measuring temperature.

- A thermometer measures heat, indicating how hot or cold something is.

- The ………. form consists of a ………. tube with a fine ……….

- This describes the basic structure of a thermometer.

- One end of the ………… is blown to form …………… bulb and the other is closed.

- This means one end of the tube is shaped into a bulb and sealed.

- Option 1: Boar

- Boar refers to a wild pig, not relevant here.

- Option 2: Cavity

- Cavity is a space within a solid object, which doesn't fit here.

- Option 3: Mole

- Mole is a unit in chemistry, not suitable here.

- Option 4: Bore

- Bore refers to the hollow part inside the tube, making it the right choice for the tube's description.