Proponents of the school of thought positing that the Americas were

Proponents of the school of thought positing that the Americas were peopled more than 15,000 years ago by a group forced to traverse thousands of miles of ice fields have themselves had to overcome obstacles in trying to account for such an improbable journey, yet those who argue that such a trek was indeed impossible and thus the first peopling of the Americas happened much later have had to account for the presence of artifacts in southern Chile that indicate that the New World was inhabited over 15,000 years ago.

A) in trying to account for such an improbable journey, yet those who argue that such a trek was indeed impossible and thus the first peopling of the Americas happened much later have had to
B) by trying to account for such an improbable journey, yet those who argue such a trek was indeed impossible and thus the first peopling of the Americas happened much later have to
C) in trying to account for such an improbable journey, whereas those arguing that such a trek was indeed impossible and that the first peopling of the Americas happened much later have themselves to
D) in trying to account for such an improbable journey, whereas those that argue that such a trek was indeed impossible and the first peopling of the Americas happened much later have had to
E) by trying to account for such an improbable journey, yet those arguing that such a trek was indeed impossible and thus that the first peopling of the Americas happened much later, they have to