Which shows a decrease in fluid pressure

The complete question is given below:

Which shows a decrease in fluid pressure? A. A fan is turned from high speed to low speed. B. Oxygen is compressed as it is put into a pressurized tank. C. Water in a creek slows down as it enters a slow-moving river. D. A river speeds up when it moves into a narrower channel.

D. A river speeds up when it moves into a narrower channel.

Explanation: The alternative A and C are not related to the question. In alternative B, oxygen can be a fluid which exerts pressure, but in the situation described, the gas is compressed in a tank. According to the Ideal Gas Law, if you compress a gas, which means you are decreasing the gas volume, the pressure will increase. So, it is not the right answer.

The letter D is the right alternative because of Bernoulli's Principle. It shows that as the speed of a moving fluid increases, the pressure within the fluid decreases. And it happens because the fluid (or in this case, the river) has the following qualities: flows smoothly, without any swirls, everywhere through the channel and the fluid has the same density everywhere.