Step 1: In a right triangle, the sum of the angles is \( 180^\circ \), and since \( \angle C = 90^\circ \), we have:
\[
A + B = 90^\circ
\]
Step 2: Using the identity \( \sin(90^\circ) = 1 \), we get:
\[
\sin(A + B) = \sin 90^\circ = 1
\]
Thus, the correct answer is \( \boxed{1} \).