I don't understand what is wrong with option C. But, also option E seems correct to me.

Where are the mistakes? Experts, may you help us?

Hello!

Let's go through each option and look at what's good/bad about them:

In the 1970s word leaked that the Tuskegee Institute had performed experiments in which researchers withheld medicine from African American males with syphilis in order to learn how the disease progresses, and in the process, the researchers had caused the deaths of dozens of men.

A) had performed experiments in which researchers withheld medicine from African American males with syphilis in order to learn how the disease progresses, and in the process, the researchers had caused the deaths of dozens of men.

A is the correct answer, so we'll leave this one alone. It's clear who killed who here.

B) had performed experiments in which researchers withheld the medicine necessary to survive syphilis from many African American males in order to learn how the disease progresses, killing dozens of them.

The modifier, "killing dozens of them," is not placed directly next to what it's referring to (African American males). By leaving the modifier at the end, it's unclear whether dozens of African American males were killed, or dozens of researchers. I know you can probably figure it out using common sense, but if you read it literally as is, it's not clear enough.

C) had performed experiments on African American males in which researchers killed dozens by receiving the incorrect treatment for syphilis from the researchers so that they could learn how the disease progresses.

The modifier "by receiving the incorrect treatment for syphilis" is placed most closely after "researchers," suggesting that the researchers killed dozens of people when the researchers were given the wrong treatment. Since we know the African American males were given treatment, not the researchers, we know this isn't written clearly.

D) had performed experiments on African American males in which researchers killed dozens from receiving the incorrect treatment for syphilis from the researchers so that researchers could learn how the disease progresses.

This one is incorrect because it uses the phrase "from receiving" which doesn't make any sense. You can kill someone by receiving, but killing them from receiving just doesn't work.

E) had performed experiments in which researchers withheld medicine from African American males with syphilis in order to learn how the disease progresses and causing the deaths of dozens of men.

This one is close to correct, but at the end it states that this practice caused the deaths of "dozens of men." Which men? The African American males with syphilis? The researchers? Other men in the future? Since it's not explicitly clear, it's incorrect. Again, I know you could probably deduce who "men" is referring to, but you shouldn't have to do so much work - it's on the writer to give you all the details as clearly as possible!

I hope this helps! I'm available if you need any follow up.