1. A dot is one-dimensional.

Question

2. A surface is two-dimensional.
3. A cube is three-dimensional.

4. At is one-dimension.
5. At is the first dimension.

6. On is two-dimensions.
7. On is the second dimension.
8. On is two dimensions.

9. In is three-dimension.
10. In is three dimensions.
11. In is the third dimension.
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Which ones do we have to use?

Answer 1

The ones that make sense are #1, #2, #3, #9 should read... It is in three dimensions
#10 should read ... It is in three dimensions
#11 should read... It is in the third dimension. That is, the z-coordinate is in the third dimension.
Hope this helps : )