The answer is C because my friend has told me it.
Answer:
It's a parallelogram, angles B and D, and A and C are congruent, lines AB and DC, and BC and AD are congruent.
Step-by-step explanation:
The surface (call it
) is a triangle with vertices at the points



Parameterize
by

with
and
. Take the normal vector to
to be

Then the flux of
across
is


