Conclusion

What we see: An assumption question. We need the unstated belief that the researchers' conclusion depends on.

Step 1. Find the conclusion and the evidence.
What we see: "So these medical researchers are convinced that the virus responsible for aphroditis melancholias is very similar to that responsible for metaeritocas polymanias."
What it means: that is the conclusion, about the cause (the virus). The evidence is that the two diseases share symptoms and incubation time.
What we do and why: we separate the two, because the assumption always sits in the gap between the evidence and the conclusion.

Step 2. Spot the gap.
What we see: the evidence is about symptoms. The conclusion is about causes.
What it means: the argument jumps from "same symptoms" to "same cause".
What we do and why: that jump only works if similar symptoms mean similar causes. That is the hidden belief we look for in the choices.

Step 3. Test the choices.
What we see: one choice is about which disease is more dangerous, one about cures, one about the goal of technology, one about who catches the disease.
What it means: none of those links symptoms to causes, so the argument does not need them.
What we do and why: only one choice bridges the gap: "diseases with similar symptoms will have similar causes."

The trap: A, because it names both diseases. How serious a disease is says nothing about whether two diseases share a cause.
Faster way: spot the word that changes between evidence and conclusion (symptoms becomes cause), then pick the choice that connects exactly those two words.
Takeaway: when the evidence talks about one thing and the conclusion about another, the assumption is the bridge between them.

Answer: E