Which of the following is an example of commensalism?
a bird is hunted, killed, and eaten by a cat.
a bird eats berries, then spreads the seeds.
a bird finds an existing hole in a tree and builds a nest in it.
a bird finds a small shellfish on a beach, cracks its shell, and eats it.

It may seem strange that the selected velocity does not depend on either the mass or the charge of the particle. (for example, would the velocity of a neutral particle be selected by passage through this device? ) the explanation of this is that the mass and the charge control the resolution of the device--particles with the wrong velocity will be accelerated away from the straight line and will not pass through the exit slit. if the acceleration depends strongly on the velocity, then particles with just slightly wrong velocities will feel a substantial transverse acceleration and will not exit the selector. because the acc