Okay let me just clarify things because you have walked in here with a confusing question in the title which does not relate to what you said in your post, which is further less related to what the actual question asks.
As per my previous reply, if you have a set of data with x-coordinates (in increasing order) as
x1,x2,x3,...,xn then you can connect neighbouring points
xi and
xi+1 with a straight line. Doing so for all neighbouring points yields a continuous curve (see the link in my last post) which is used to predict data within its range (this is interpolation).
As for the question, part (b) just wants you to use this idea that if the points are not connected to their neighbours, then it becomes rather confusing as to which line to use to interpolate. E.g. for (a)(ii) there are three possible answers.
For part (c), I cannot think of a scenario where a graph like the one in question would be useful. It might indicate some order in which the speakers were tested though.