1. They are eating cotton candy.

2. They are eating cotton candies.
3. They are eating a cotton candy.
4. The boy is eating two cotton
candies.

(Which one is correct?)

Only 1 is correct.

Here's a photo of a girl eating cotton candy.

http://www.mikesbaby.com/images/year3/cotton-candy.jpg

it is b

Out of the given options, the correct sentence would be: "They are eating cotton candy."

Here's why:

1. "They are eating cotton candy." : This sentence is the correct form when referring to multiple individuals consuming a single cotton candy. In this sentence, the noun "cotton candy" is not pluralized because it is being used as a mass noun, indicating the substance itself rather than individual pieces.

2. "They are eating cotton candies." : This sentence is incorrect because it pluralizes the noun "cotton candy" to "cotton candies", indicating that each person is eating multiple cotton candies. However, in the context of the sentence, it seems like they are collectively sharing and eating one cotton candy.

3. "They are eating a cotton candy." : This sentence is incorrect because it uses the indefinite article "a" with the noun "cotton candy". "A" implies singularity, but in this context, it suggests that they are only eating a single piece of cotton candy, which is not's what was intended.

4. "The boy is eating two cotton candies." : This sentence is incorrect because it specifically mentions the boy eating two cotton candies, while the question asks about a plural reference to a group of people.