Which choice most effectively combines sentences 5 and 6 (reproduced below) at the underlined portion?
A spider of this species was discovered in the Erg Chebbi. It is a sandy desert in southeastern Morocco.

A comma after “Chebbi” makes clear that what follows in the sentence (“a sandy desert in southeastern Morocco”) describes Erg Chebbi. Choice B is incorrect because a dash followed by “this being” is an awkward and unnecessarily dramatic way to combine sentences 5 and 6. Choices C and D are incorrect because each introduces repetition of “Erg Chebbi” into the combined sentence