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1. There are much nicer shops in the town center.

2. There are many nicer shops in the town center.

3. There are much prettier girls in this class.

4. There are many prettier girls in this class.

5. There are much more beautiful girls in this class.

6. There are many more beautiful girls in this class.

Which of the above sentences is NOT acceptable?
Comments  
None of them is unacceptable. They are all correct.
Note the parsing:
There are [much prettier] girls in this class. (There are some girls who are not just prettier, but much prettier)
There are [many] [prettier] girls in this class. ( There are many girls who are prettier -- but not necessarily much prettier)
There are [many] [much prettier] girls in this class. (There are many, and they are much prettier.)
CJ
How about the following two sentences?

7. There are much more girls in this class.

8. There are many more girls in this class.
Students: We have free audio pronunciation exercises.
Use "many more" for a countable noun like that.

There are a significantly larger number of girls in this class.
There are many more beautiful girls in this class.

What does the above sentence mean?

(A) There are a lot of prettier girls in this class.
(B) There are a lot more pretty girls in this class.
"There are many [more beautiful] girls in this class."
"There are [many more] beautiful girls in this class."

I'd say you could only determine the exact meaning of that sentence based on the way it's spoken. The speaker would pause slightly and/or add stress to a particular word or words in order to indicate the parsing. So, if the meaning were "a lot of girls who are more beautiful", the speaker might pause slightly between the words 'many' and 'more' and also add stress to the word 'many'.
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Teo1. There are much nicer shops in the town center.X

2. There are many nicer shops in the town center.

3. There are much prettier girls in this class.X

4. There are many prettier girls in this class.

5. There are much more beautiful girls in this class.X

6. There are many more beautiful girls in this class.

Which of the above sentences is NOT acceptable?

Anon, do you not see that "much nicer" can describe the type of shop, not the relative number?

Please see the posts by CalifJim and Yankee earlier in the thread.