Refer to figure.
Static pressure is a result of the weight of air in the atmosphere. This pressure acts equally in all directions on the aircraft. This pressure acts on all bodies in the atmosphere.

The pitot tube is the device used aboard aircraft to measure the dynamic pressure. As an aircraft moves through the air, the front surfaces experience an increased pressure, as a result of the aircraft's kinetic energy. Relative to the aircraft, when flowing air is brought to a complete stop, the pressure will be equal to the total (or "stagnation") pressure - this will be the sum of the static pressure and the dynamic pressure:

Total pressure = Static pressure + Dynamic pressure
P_T = P_S + ½ρV²

The front of the pitot tube is aligned with the direction of flight. When air enters the tube, it comes to a stop - and the stagnation pressure is measured. By subtracting the effect of static pressure (from a separate static port) - we are left with only the dynamic pressure!

The dynamic pressure is a result of moving through the air, and so the ASI (airspeed indicator) is calibrated to convert dynamic pressure readings into an airspeed, usually in knots. It does this assuming a density of 1.225 kg/m³, although air density changes significantly with altitude and different weather conditions, which leads to errors in what's called the "Indicated Airspeed" (IAS).

Via the static port. → INCORRECT.

• The static port is positioned in a way such that it will not sense dynamic pressure, and only static pressure

Via the alternate static port. → INCORRECT.

• An alternate static port also only measures static pressure. It is usually located in the cabin (non-pressurised aircraft), incase the external static port becomes blocked.

Via the VSI (Vertical Speed Indicator). → INCORRECT.

• The VSI is an instrument - not a measurement system. It measures how rapidly the static pressure is changing, and so also does not measure dynamic pressure.

Using the pitot tube, subtracting the effect of static pressure → CORRECT.