**A**
It is a plot of the Riemann zeta function on the boundary
of the rectangle [0.4,0.6]+[0,14.5]*i* in the complex plane.
Since the contour winds around the origin once
(and the rectangle does not contain the point *s*=1,
which is the unique pole of zeta(*s*)),
the zeta function has a unique zero inside this rectangle.
Since the complex zeros are known to be symmetric about the line
Re(*s*)=1/2, this zero must have real part exactly equal 1/2,
in accordance with the Riemann hypothesis.

It is known that this first “nontrivial zero” of zeta(*s*)
occurs at *s*=1/2+*it* for *t*=14.13472514...
The pole at *s*=1 accounts for the wide swath
in the third quadrant, which corresponds to *s*
of imaginary part less than 1.