This question is asking you to do two things. First, you need to identify the conclusion in the argument, and then you need to find an answer choice which re-states that conclusion. Whenever you are stumped on a logical reasoning question, the best thing you can do is break the argument down into its component parts. Here's a breakdown of the argument:
Premise: Adobe conducts heat slowly, so it retains heat during the evenings but stays cool during the day. Premise: Houses made of different building materials conduct heat and grow hot during the day and cold at night. Conclusion: Adobe is an ideal material for building in the desert.
Answer Choices: (A) is incorrect. There are a few different ways to eliminate this option. First, the conclusion is much simpler than this, as it just tells us that adobe is good for the desert. This answer choice gives us far more information. Second, the argument does not talk about a concept such as a "suitable substitute." Finally, this answer choice doesn't even mention the desert.
(E) is correct. This answer choice simply rephrases the conclusion above.