Ok, a British native teacher said in his English class "What do you think are the advantages of online dating?".
My question is why he used the word "are".
Why not "What do you think about the advantages of online dating?"
Those two questions have quite different meanings. The first one:
What do you think are the advantages of online dating?
is asking the students to list what they consider to be the advantages of online dating. (Though the return question of "Compared to what?" comes to mind. And as someone who has been through that process, I can assure you that the advantages compared to celibacy, solitude and a good book are all too often hard to identify, but that's wandering off topic.) You can't say "compared to traditional dating", since "traditional" is a very cultural-specific thing. What is traditional for someone from a Sri Lankan background will be very different to what is traditional for someone from Washington.
On the other hand:
What do you think about the advantages of online dating?
would be asking for the students' opinion about those advantages, not what those advantages supposedly are. Since the advantages have not been identified in the second question, it would seem to be even more imprecise than the first one.
I think that the first question is correct, if somewhat loose in its terms of reference.
I mostly agree with Alan K's answer. I'll mention the differences that I see. .
"What do you think are the advantages of online dating?"
This question can be rewritten as follows:
"What are the advantages of online dating do you think?"
The main question is, "What are the advantages of online dating?" The teacher's reason for adding 'do you think' is that many students are used to accepting and quoting received wisdom. They have learned to rely on the opinions of so-called experts and to believe that the experts are necessarily correct. By adding the rider 'do you think', the teacher is seeking to avoid this and encourage the student to formulate their own opinions.
What do you think about the advantages of online dating?
This is a different question. It assumes (a) that there are advantages and (b) that the student should already know what those advantages are.
That question encourages a formulaic answer. The student is expected to list the usual reasons and then comment on them.
What if we ask the question differently: What do you think the advantages and disadvantages of online dating are? As long as the rule says when combining two questions, the second one changes into a statement!