3. If the lengths of three line segments $a, b, c$ satisfy $\frac{b}{a}=\frac{c}{b}=\frac{\sqrt{5}-1}{2}$, then $(a, b, c)$ is called a "golden segment group". The three line segments in a golden segment group ( ).
(A) can form an acute triangle
(B) can form a right triangle
(C) can form an obtuse triangle
(D) cannot form a right triangle
3. (D).

Let $k=\frac{\sqrt{5}-1}{2}$, then $k^{2}+k=1$.
Given $\frac{b}{a}=\frac{c}{b}=k$, we have $b=k a, c=k^{2} a$. Since $b+c=\left(k+k^{2}\right) a=a$,
therefore $a, b, c$ cannot form a triangle.