下列哪个图形的阴影部分占 25%？

1. Convert the required percentage to a fraction

$25\% = \frac{25}{100} = \frac{1}{4}$

2. Analyse Figure (1)

Figure (1) is divided into $8$ equal triangles. $2$ are shaded.
Fraction shaded = $\frac{2}{8} = \frac{1}{4} = 25\%$.

3. Analyse the other figures to confirm

Figure (2): $5$ out of $16$ equal squares are shaded ($\frac{5}{16} \neq \frac{1}{4}$).
Figure (3): $1$ out of $4$ strips is shaded, but the strips are not equal in area, so it is not $\frac{1}{4}$.
Figure (4): $1$ out of $5$ equal sectors is shaded ($\frac{1}{5} = 20\% \neq 25\%$).