Question 1040235
  *[illustration d79d34cacc.png]
<pre><b>
[Notice about the above graphs:  On the far left end, 
the x-coordinates are all {{{-3pi/2}}}, and on the right
end they are {{{3pi/2}}}, as those are partly cut off the
pictures.]

A is clearly periodic.  The first period
starts at {{{-3pi/2}}} and ends at {{{-pi/4}}}.
Then at {{{-pi/4}}} it starts repeating that exact same 
figure and ends it at {{{pi}}}.  Then it starts again at
{{{pi}}} and it is assumed top repeat that figure over
and over indefinitely.

C is clearly periodic. At {{{pi/2}}} it starts repeating
the same figure as the figure between {{{-3pi/2}}} to {{{pi/2}}}.

D is very clearly periodic.  It repeats the same v-shape
over and over.

B is NOT periodic because it does not repeat the same figure
at all.

Edwin</pre></b>