But how to assess the polarity of #""^(-delta)X-H^(delta+)#. The most convenient means would be to look up the Pauling electronegativities, which measure the ability of an atom in a chemical bond to polarize electron density towards itself. We know that electronegativity INCREASES across a Period (from left to right as we face the Periodic Table), and DECREASES down a Group. And so #A# qualifies on this basis.
As background we can quote the Pauling electronegativities (of course these will not be available to you in an exam):
#H(2.1);C(2.2);N(3.0);O(3.5)#
And #Delta_"electronegativity"# is greatest for #(A)#. And of these bonds only #N-H#, and #O-H# are polar.
