The current theory about earthquakes holds that they are caused by adjoining plates of rock sliding past each other; the plates are pressed together until powerful forces overcome the resistance. As plausible as this may sound, at least one thing remains mysterious on this theory. The overcoming of such resistance should create enormous amounts of heat. But so far no increases in temperature unrelated to weather have been detected following earthquakes.

Summarize Argument: Causal Explanation
The author claims that the current theory about earthquakes doesn’t fully explain the results we observe when earthquakes happen. This is supported by an example of the theory not matching reality. The theory predicts that earthquakes should generate a lot of heat, but in practice no earthquake-related temperature increases have been observed. That does sound mysterious.

Identify Conclusion
The author’s conclusion is that the current theory still leaves at least one aspect of earthquakes “mysterious” in that the theory’s predictions don’t quite match the actual data.

A
No increases in temperature have been detected following earthquakes.
The argument states this claim as a fact, and does not provide any support for it, which means it’s not a conclusion. Instead, this is used to support the conclusion that the current theory is incomplete.
B
The current theory does not fully explain earthquake data.
This is exactly what the author is trying to say. The conclusion that the theory leaves something “mysterious” just means that it doesn’t fully explain observed data. The discussion of temperature supports this with a concrete example.
C
No one will ever be sure what the true cause of earthquakes is.
This is not stated in the argument. The author never claims that earthquakes are impossible to understand, just that the current theory isn’t 100% perfectly complete.
D
Earthquakes produce enormous amounts of heat that have so far gone undetected.
This is not stated in the argument. The author only establishes that a mystery exists, but does not suggest any possible explanations for what might resolve the mystery.
E
Contrary to the current theory, earthquakes are not caused by adjoining plates of rock sliding past one another.
This is not stated in the argument. The author never claims that the current theory is fundamentally incorrect, just that it still needs improvement to explain every aspect of earthquake data.

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