Explanation: This question describes the specific construction of a **stripline** transmission line. Stripline consists of a flat, narrow conductor (the "center conductor") positioned *between* two parallel ground planes, separated by a dielectric material. This configuration provides good shielding and consistent characteristic impedance at microwave frequencies. **Microstrip** (A) is similar but uses a single ground plane below the conductor, not two ground planes surrounding it. **Coax** (B) uses a central conductor surrounded by a dielectric and an outer cylindrical conductor (shield), a different geometry entirely. **Waveguide** (D) is a hollow metallic tube that guides electromagnetic waves without a central conductor, primarily used at much higher microwave frequencies.