Correct answer: (a) Electric plane tested by NASA
Explanation
- A
Electric plane tested by NASA
Electric plane tested by NASA. Greased Lightning-10 (GL-10) is a NASA Langley remotely piloted hybrid-electric VTOL demonstrator with tilting wings and multiple propellers. That stored letter is the official key.
- B
Solar-powered two-seater aircraft designed by Japan
Solar two-seater from Japan. That does not name GL-10. This letter is not the key.
- C
Space observatory launched by China
Chinese space observatory. Unrelated to the NASA aircraft. This letter is not the key.
- D
Reusable rocket designed by ISRO
ISRO reusable rocket. ISRO RLV-TD is a different programme. This letter is not the key.
Summary. Official key is (a) electric plane tested by NASA. GL-10 Greased Lightning is a hybrid-electric VTOL UAV, not a Japanese solar tourer, a Chinese observatory or an ISRO rocket. Honour the stored letter (a).