Your shoulders are not supposed to touch the backrest when driving. However, if they do it’s not a huge deal. You wouldn’t be arrested for it.
The decrease of what? The way you worded the question makes absolutely no sense to me.
D. a sample of 1,000 people called at random from the telephone book
The reason time is important is b/c if there’s too much delay in between the U.C.S and the C.S the learner may not make the connection. For acquisition you must introduced the C.S and as soon as thats presented quickly introduce the U.C.S so there is an overlap between those two