Question

Dostoevsky, whose novels plumbed highly philosophical themes, **Nietzsche had a background in classical philology that gave him a unique perspective toward the Western Philosophical tradition, and the Danish Christian writer Kierkegaard were considered the founders** of Existentialism.
(A) Nietzsche had a background in classical philology that gave him a unique perspective toward the Western Philosophical tradition, and the Danish Christian writer Kierkegaard were considered the founders
(B) Nietzsche had a background in classical philology giving him a unique perspective toward the Western Philosophical tradition, and the Danish Christian writer Kierkegaard was considered the founder
(C) Nietzsche, whose background in classical philology gave him a unique perspective on the Western Philosophical tradition, and the Danish Christian writer Kierkegaard was considered the founder
(D) Nietzsche, whose background in classical philology gave him a unique perspective on the Western Philosophical tradition, and the Danish Christian writer Kierkegaard were considered the founders
(E) Nietzsche, who had had a background in classical philology that was giving him a unique perspective with the Western Philosophical tradition, and the Danish Christian writer Kierkegaard was considered the founder

Answer 1

"Was considered the founder" is incorrect hence B,C,E are out .. between A and D, A is clearly out because of missing parallelism
Hence D is the only choice left

Answer 2

Founders needed so kill B C E...kill A for parallelism.