ANS:A - pitot tube

The speed of a submarine in deep sea and that of an aeroplane are typically measured by a pitot tube. A pitot tube is a device used to measure fluid flow velocity, particularly in air or water. It works based on the principle of Bernoulli's equation, which relates the pressure difference between static and dynamic pressure to the velocity of the fluid. In the case of an aeroplane, the pitot tube measures the dynamic pressure of the air flowing around the aircraft, which is related to its airspeed. Similarly, in the case of a submarine, the pitot tube can measure the dynamic pressure of the water flow around the vessel, which can be related to its speed.