[skip this next bit if you're not interested in the details but just want to help me out]
An example of dependent plurality is the following. In the sentence Cars have wheels, wheels is in the plural form because individual cars have multiple wheels. But in the sentence Humans have noses, noses isn't in the plural form because individual humans have multiple noses (they obviously don't), but because humans is plural and noses 'depends' on humans. In other words, if there are multiple humans, there must also be multiple noses, so noses takes the plural form as well.
If you're a speaker of English this may sound obvious to you, but in Dutch, for example, the most natural-sounding equivalent of the second sentence would translate as Humans have a nose, using a singular - after all, individual humans have only a single nose.
In some varieties of English (or to some individual speakers), Humans have a nose is OK as well.
A fellow linguist told me that in Greek, which also requires dependent plurals, certain factors might influence the strength of this requirement. For example, you can't say (in Greek) that The students got a high grade unless they all got the same grade: you have to say The students got high grades. However, using the singular form becomes (sort of) OK if you continue the sentence in some way - say, The students got a high grade but they still weren't happy.
This made me wonder whether similar things might influence the need for a dependent plural in English.
[now here comes the important bit :)]
So, native speakers of English, it would be lovely if you could tell me, for the next three pairs of sentences
(1) if any of the two is markedly better than the other
(2) if so, how much better it is - is the difference tiny (one of the sentences just sounds a bit odd) or huge (one of the sentences is completely ungrammatical) or somewhere in between?
(a) The girls are wearing blue dresses.
(b) The girls are wearing a blue dress.
pair 2 (used in a situation where each girl has a different boyfriend):
(a) The girls kissed their boyfriends.
(b) The girls kissed their boyfriend.
pair 3 (again, each girl has a different boyfriend):
(a) The girls will be jealous if someone else kisses their boyfriends.
(b) The girls will be jealous if someone else kisses their boyfriend.
Oh and if you could mention where you are from / which variety of English you speak, it would be helpful as well :)
Thanks a bunch!