D. 1/4
Explanation:
a perfect square is written in the form
\((x+a)^2 = x^2 + 2ax +a^2\) (1)
In our problem, we have this perfect square:
\(x^2 - x + C\) (2)
with C being unknown. However, by comparing (1) and (2), we know that
\(2a=-1\)
So, we find
\(a=-\frac{1}{2}\)
and therefore, the missing term must be
\(a^2 = \frac{1}{4}\)
so the complete square is
\(x^2 -x +\frac{1}{4}\)
