The point of my observations should be quite clear by now, namely that Joseph Conrad was a thoroughgoing racist. That this simple truth is glossed over in criticisms of his work is due to the fact that white racism against Africa is such a normal way of thinking that its manifestations go completely unremarked. Students of Heart of Darkness will often tell you that Conrad is concerned not so much with Africa as with the deterioration of one European mind caused by solitude and sickness. They will point out to you that Conrad is, if anything, less charitable to the Europeans in the story than he is to the natives, that the point of the story is to ridicule Europe's civilizing mission in Africa. A Conrad student informed me in Scotland that Africa is merely a setting for the disintegration of the mind of Mr. Kurtz. –“An Image of Africa: Racism in Conrad's
Heart of Darkness,”
Chinua Achebe

What is Achebe’s claim in this excerpt?

Conrad’s writing focuses on solitude and sickness, not on clashing cultures or belief systems.
Conrad’s depiction of Europeans is biased and mostly negative, and his work should not be read as a result.
Conrad uses Africa mostly as a setting to show how separation and solitude lead the human mind to disintegrate.
Conrad and literary critics of his text have racist viewpoints because they fail to see the dehumanizing depiction of Africans in the text.