Why does B fail to explain the differences between the two groups ?

I was wondering why B is the answer ? I thought C was a good answer at first but I think I understand why it isn't. Is it because if technological innovations were imported to Australia more recently than 10,000 years ago, meaning after the land bridge disappeared, wouldn't that make it harder to argue that there were differences between the two groups because the innovations that the Tasmanians had were imported to Australia after the bridge disappeared ? Could you also explain why B is a better answer ? If the innovations were developed by Tasmanians more than 10,000 years ago, how can you argue that differences between the two groups emerged two thousand years after the bridge disappeared ?