The correct answer is (b), Ginkgo biloba.
A living fossil is a species that has remained relatively unchanged over a long period of time, often millions of years. Ginkgo biloba is a living fossil because it has been around for over 200 million years and has changed very little in that time. It is the only surviving member of its genus and family, and it is one of the oldest living tree species.
Cedrus deodara, Gnetum gnemon, and Ephedra foliata are all living plants, but they are not considered to be living fossils. Cedrus deodara is a species of cedar tree that is native to the Himalayas. Gnetum gnemon is a tropical plant that is native to Southeast Asia. Ephedra foliata is a shrub that is native to North America.
All of these plants are important members of their ecosystems, but they are not as old as Ginkgo biloba and have not changed as little over time.