3. Let $E_{i} F_{i}(i=1,2,3,4)$ be line segments parallel to the upper and lower bases of a trapezoid and whose endpoints lie on the legs of the trapezoid. If $E_{1} F_{1}$ divides the trapezoid into two equal areas, $E_{2} F_{2}$ is the midline of the trapezoid, $E_{3} F_{3}$ divides the trapezoid into two similar figures, and $E_{4} F_{4}$ passes through the intersection of the diagonals of the trapezoid, then their size relationship is ( ).
(A) $E_{1} F_{1} \leqslant E_{2} F_{2} \leqslant E_{4} F_{4} \leqslant E_{3} F_{3}$
(B) $E_{4} F_{4} \leqslant E_{3} F_{3} \leqslant E_{2} F_{2} \leqslant E_{1} F_{1}$
(C) $E_{2} F_{2} \leqslant E_{1} F_{1} \leqslant E_{4} F_{4} \leqslant E_{3} F_{3}$
(D) $E_{1} F_{1} \leqslant E_{4} F_{4} \leqslant E_{3} F_{3} \leqslant E_{2} F_{2}$
3. B.

Let the upper and lower bases of the trapezoid be $a_{1}$ and $a_{2}$. Then
$$
\begin{array}{l}
E_{4} F_{4}=\frac{2 a_{1} a_{2}}{a_{1}+a_{2}}, E_{3} F_{3}=\sqrt{a_{1} a_{2}}, \\
E_{2} F_{2}=\frac{a_{1}+a_{2}}{2}, E_{1} F_{1}=\sqrt{\frac{a_{1}^{2}+a_{2}^{2}}{2}} .
\end{array}
$$