Vaneless electric fans are safer than traditional electric fans because

(1) Comparing the structures of the bladeless electric fan and the traditional vane electric fan, it can be seen that the bladeless electric fan is safer than the traditional vane electric fan because there are no blades;

(2) The motor sucks air from the air inlet, and the sucked air enters the annular cavity after being compressed, and then it is blown out from the slit on the annular cavity at high speed, carrying the surrounding air forward, resulting in more air flowing into the air outlet of the rear fan, and the air volume is obviously enlarged. Therefore, when the fan operates normally, the air quality passing through the air outlet is greater than the air quality flowing into the air inlet at the same time.

(3) Air is blown out from the slit in the annular cavity at high speed, and the wind speed is high and the pressure is low, so more air flows into the fan outlet, that is, the principle of the relationship between fluid pressure and flow rate is applied.

A, the truck is equipped with many wheels, and it is irrelevant to reduce the pressure on the ground by increasing the stress area;

B, when the plane flies, the air above the wing has a high speed and a low pressure, and the air below has a low speed and a high pressure, so that the plane can get lift, which is in line with the meaning of the question;

C. The yacht floats on the sea surface. Because of the buoyancy and gravity of the sea, these two forces are equal in magnitude and opposite in direction, making the yacht float on the water surface.

D it doesn't matter that the ship sails from upstream to downstream through the lock, using the connecting body principle;

So choose B.

(4) Compressed air is blown out from the slit in the annular cavity at a high speed, and the pressure is low where the flow speed is high, and the surrounding air flows forward together, resulting in more air flowing into the air outlet of the electric fan at the back, and the air volume is obviously enlarged.

So the answer is: (1) No fan blades; (2) greater than; (3)B； (4) Where the speed is high, the pressure is low.