KPSS 2017-1 Soru=22

A perennially contentious issue in English is the search
for a gender-neutral third-person singular pronoun.
Generally, he is taken as the default, as in “If someone
calls, let him know I’ll be back at 3 p.m.” ---- He or
she is long and complicated, and constructs like s/he
or (s)he or he/she have never caught on, probably
because they sound artifical (and how would you even
pronounce them?) And one, as in “One must fill in and
sign this form.” sounds literary or too formal. For some,
to change the default to she would be unthinkable.

Which of the following completes the paragraph?

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