Use the Following Description to Answer the Question

Use the following description to answer the question.
On the volcanic, equatorial West African island of Sao Tomé, two species of fruit fly exist. Drosophila yakuba inhabits the island's lowlands and is also found on the African mainland, located about 320 kilometres away. At higher elevations, and only on Sao Tomé, is found the very closely related Drosophila santomea. The two species can hybridise, though male hybrids are sterile. A hybrid zone exists at middle elevations, though hybrids there are greatly outnumbered by D. santomea. Studies of the two species' nuclear genomes reveal that D. yakuba on the island is more closely related to mainland D. yakuba than to D. santomea (2n = 4 in both species) . Sao Tomé rose from the Atlantic Ocean about 14 million years ago.
The observation that island D. yakuba are more closely related to mainland D. yakuba than island D. yakuba are to D. santomea is best explained by proposing that D. santomea ________.

A) descended from a now-extinct, non-African fruit fly
B) arrived on the island before D. yakuba
C) descended from a single colony of D. yakuba, which had been introduced from elsewhere, with no subsequent colonisation events
D) descended from an original colony of D. yakuba, of which there are no surviving members. The current island D. yakuba represent a second colonisation event from elsewhere