What is the correct way to write sentences 23 and 24?

F Many of the species that once made their home on Madagascar are now extinct, scientists, however, are still making discoveries.

G Although many of the species that once made their home on Madagascar are now extinct and scientists are still making discoveries.

H Many of the species that once made their home on Madagascar are now extinct, but there are scientists. Who are still making discoveries.

J Although many of the species that once made their home on Madagascar are now extinct, scientists are still making discoveries.