The correct answer is: A. absolute pressure sensor.
An absolute pressure sensor measures the pressure relative to perfect vacuum. This means that the sensor will read zero when there is no pressure at all, such as in outer space.
A gauge pressure sensor measures the pressure relative to the ambient pressure. This means that the sensor will read zero when the pressure is equal to the ambient pressure, such as when the sensor is in a room with normal air pressure.
A vacuum pressure sensor measures the pressure below the ambient pressure. This means that the sensor will read a negative number when the pressure is less than the ambient pressure, such as when the sensor is in a vacuum chamber.
A differential pressure sensor measures the difference between two pressures. This means that the sensor will read the difference between the pressure on one side of the sensor and the pressure on the other side of the sensor.