Psychologist: Thinking can occur without language.
Main Conclusion
Thinking can occur without language.
Intermediate Conclusion (thus)
A thought of a typical human face must exist in the infants' minds.
Evidence
In a study, 3 month old infants, who obviously have no language, can detect irregular photos, ones that don't match their internal representation of what a human face should look like.
Evaluate
Whenever we read Main Conclusion and Role, we remind ourselves that the Main Conclusion is usually not the last claim. It's usually earlier than the Support. And, specifically, it's usually the First Sentence or a Rebuttal.
Reminding ourselves of that tendency before we read the argument on Role / Main Conclusion helps us interpret the first sentence as the main conclusion. It doesn't sound like some obvious author opinion, but it does sound like a general statement that the paragraph starts to defend with research.
The last sentence has an obvious conclusion indicator attached (Thus), but we know that Role is super famous for Intermediate Conclusions, so we want to consider whether this "Thus" is indicating the main conclusion or an intermediate one.
The final claim supports the first claim. Since an infant, who doesn't have language, has the thought of a typical human face, this shows that thinking can occur without language.
Goal
We're being asked about this final claim. We know it's a conclusion, because it's prefaced by "Thus". But in this case it's an intermediate / subsidiary conclusion. It's supported by the 2nd and 3rd sentences, but it supports the 1st sentence.