With which method of sampling does every memeber of all parts of the population have an equal chance of being selected?

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.

Let x have probability generating function gx (s) and let un generating function u(s) of the sequence uo, u1, satisfies p(x > n). show that the (1- s)u(s) = 1 - gx(s), whenever the series defining these generating functions converge.

Dana kicks a soccer ball. the table shows the height of the soccer ball with respect to the time, in seconds, after the ball was kicked. time | height(seconds) | (feet) ~0.5 211 341.5 392 362.5 253 6which graph best displays the relationship shown in the table? (i just need confirmation that its c)