I think eating genetically engineered foods are not harmful at all.

I think eating genetically engineered food is not harmful at all.

I think eating genetically modified foods are not harmful at all.

I think eating genetically modified food is not harmful at all.

I think eating GM foods are not harmful at all.
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Are all the expressions above correct? which expressions are commonly used?

Only the second and fourth sentences are correct. The word "eating" (a gerund) is the subject and is singular, so all those sentences with "are" for the verb are incorrect.

Correction of sorts: "eating" is the subject of its own clause, not the main subject of the entire sentence.

=)

OK. Thank you. What about the form of food? Do we have to use 'food' or 'foods'?

"food" is fine -- no need to pluralize it.

1. She did her part, and the native speaker did her part. They were cooperative and did their parts properly.

2. Teachers should make students say, act out and work together in class.

3. The quality of a teacher's voice is important in teaching. If she shouts loudly to stop students' making noises, she may hurt her voice. In co-teaching both teaches' voices are essential.

4. As the Korean teacher explained what the native speaker said, students have no difficulty in working with the native speaker.

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Would you check the expressions, please?
After watching a co-teaching video, I could analyze as in the above.

All of the expressions you provided convey the same message that eating genetically engineered or genetically modified foods is not harmful. However, there are slight variations in grammar and word choice.

From a grammatical standpoint, the correct expressions would be:

1. "I think eating genetically engineered foods is not harmful at all."
2. "I think eating genetically modified food is not harmful at all."

The word "foods" in the first expression and "food" in the second expression are both plural nouns, which agrees with the verb "is" (singular form).

In terms of commonly used expressions, any of the variations you provided can be used to convey the message. The choice between "genetically engineered" and "genetically modified" may vary based on personal preference or regional conventions. Similarly, using "foods" or "food" can depend on whether you want to refer to the concept as a whole or specific types of food.

Overall, all the expressions communicate the belief that eating genetically engineered or genetically modified foods is not harmful.