What is 'Greased Lightning-10 (GL-10)', recently in the news?

1. 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.

2. 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.

3. C

   Space observatory launched by China

   Chinese space observatory. Unrelated to the NASA aircraft. This letter is not the key.

4. 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).