"What is this movie about?"
Mainly 2 ways:
1) As a pronoun of sth./sb. understood or implied.
This is a dog that sells hats.
2) As a modal particle to conclude a statement.
Turtles do not eat banana.
They should be more consistent about it, then. They miss this in their translation of "What is this business meeting mainly about?"
X 是关于什么 is also a correctly formed sentence, though the underlying grammar structure is different. That said, X 是关于什么的 is the more common form.
IMHO I cannot agree that's grammatically correct. Of course if someone says it without 的 I won't be mad. In order to speak natural sounding Chinese such tiny bits are somehow important.
Whenever we say A 是 B, both sides of 是 should be a noun, a clause or an equivalent. We cannot use a noun determinant.
这支笔是红 is wrong
we can only say
"this pen is a red one"
for saying "This pen is red".
Compare these correct sentences:
You are correct that my statement was inaccurate. As is suggested in your examples, the 是…的 is probably in fact an A 是 B sentence structure with the B noun phrase elided. You will sometimes see 是 omitted in such sentences, but not 的. I probably should not have posted so late at night! Thanks for correcting my error!
It is necessary in the sense that it makes the question less formal (since movies are casual, unlike, say, meetings).
People use it as in the example for casual, informal situations, so it's appropriate for outings with friends, but less so for meetings and work events.
Yes, except that i don't ike 个 for a movie.
If everything is counted by 个, we don't need to have classifier in Chinese.