Answer:
A
Explanation:
Doppler Echocardiogram
A traditional echocardiogram uses sound waves to produce images of the heart. In this procedure, a radiologist uses a transducer to transmit and receive ultrasound waves, which are reflected when they reach the edge of two structures with different densities. The image produced by an echocardiogram shows the edges of heart structures, but it cannot measure the speed of blood flowing through the heart. Doppler techniques must be incorporated to provide this additional information. In a Doppler echocardiogram, sound waves of a certain frequency are transmitted into the heart. The sound waves bounce off blood cells moving through the heart and blood vessels. The movement of these cells, either toward or away from the transmitted waves, results in a frequency shift that can be measured. This helps cardiologists determine the speed and direction of blood flow in the heart.
Wind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a <span>generator to create electricity.</span>
If the cell membrane were not selectively permeable, then unwanted substances would transfer through instead of being blocked out. Think of it like this: you have a sifter with various sizes of spice in it. You only want the finer grains of spice in your food, so when you shake the sifter, the larger pieces of spice don't fit through the small holes that only allow fine grains. Then you are left with the small spices in your food and the large ones stuck in the sifter.
Hopefully this helps and I wasn't too confusing :)
10 newtons (N). If the tree had less, it would be pushed. If it had more, it would push the kid (not possible).