请以资深高中物理教师的口吻和水平，详细解答这道光学题目，并给出具体的思路分析。---**Extraction Content:** **Question Stem:** 5. 某种手机防窥膜由透明介质和对光完全吸收的屏障构成，如图所示，屏障垂直于屏幕平行排列，可实现对像素单元可视角度$\theta$的控制。发光像素单元紧贴防窥膜下表面，位于相邻两屏障正中间。不考虑光的衍射，下列说法正确的是（ ） **Options:** A. 防窥膜实现防窥效果主要是靠光的**全反射** B. 其他条件不变时，透明介质的折射率越小，可视角度$\theta$越小 C. 可视角度$\theta$与屏障高度$d$无关 D. 从上往下看，看到的图像比发光像素单元位置低 **Chart/Diagram Description:** * **Type:** Schematic diagram illustrating the cross-section of a手机防窥膜 (mobile phone anti-peeping film). * **Main Elements:** * **Layers:** An upper region labeled "空气" (Air) above a region labeled "透明介质" (Transparent medium). Below the transparent medium are rectangular elements labeled "发光像素单元" (Light-emitting pixel unit). * **Shields:** Vertical, rectangular structures labeled "屏障" (Shields) embedded within the transparent medium. They are arranged in parallel rows, perpendicular to the plane of the screen. * **Light-emitting pixels:** Located below the transparent medium, beneath the gaps between the shields. Arrows indicate light rays originating from these pixels and propagating upwards. * **Anti-peeping film:** The entire structure containing the transparent medium, shields, and possibly the pixels and air boundary is labeled as "防窥膜" (Anti-peeping film) with a bracket indicating its extent vertically, and a height labeled as $d$. * **Viewing Angle ($\theta$):** A cone-shaped region originating from a point within the transparent medium (implied observer's eye position) at the top boundary. Two dashed lines extend from the edges of the gap between two shields upwards, forming an angle labeled as $2\theta$. This angle appears to represent the total viewing angle, with $\theta$ being half of this angle. * **Light Rays:** Several light rays are shown originating from the light-emitting pixels. Some rays travel straight up through the gaps between shields. Other rays travel upwards at an angle and are blocked by the shields. Two specific rays are shown originating from a pixel, passing through the edges of the gap between two shields, and meeting at a point on the top boundary within the angle $2\theta$. * **Labels:** "空气" (Air), "透明介质" (Transparent medium), "屏障" (Shield), "发光像素单元" (Light-emitting pixel unit), "防窥膜" (Anti-peeping film), $\theta$, $d$. * **Relative Position:** Shields are vertical, parallel, and positioned above the light-emitting pixels, within the transparent medium. Pixels are between adjacent shields. The transparent medium is below the air. * **Function:** The shields are stated to be light-absorbing and control the viewing angle $\theta$. Light rays that hit the shields are blocked. Only rays that pass through the gaps between the shields within a certain angle can exit. The angle $2\theta$ represents the maximum angle from which light from the pixel can exit through the specific gap. The diagram suggests this angle is determined by the width of the gap between shields and the height $d$ of the shields. Specifically, the angle $2\theta$ is subtended by the gap width at the top surface of the transparent medium. * **Units:** No specific units are indicated.