To determine which statement is true, we need to add the fractions of grass that Amar and Aayush cut.
Amar cut \( \frac{1}{6} \) of the grass, and Aayush cut \( \frac{1}{3} \) of the grass.
First, we need to convert \( \frac{1}{3} \) to a fraction with a common denominator of 6:
\[ \frac{1}{3} = \frac{2}{6} \]
Now we can add the fractions:
\[ \text{Total cut} = \frac{1}{6} + \frac{2}{6} = \frac{3}{6} = \frac{1}{2} \]
So, together the boys cut exactly half of the yard. Therefore, the correct statement is:
C. the boys cut exactly half of the yard.