The correct answer is: D. were
The sentence “I wish I were taller” is an expression of a wish or desire. In this case, the speaker is wishing that they were taller. The verb “were” is used to express a wish or desire in the past tense.
The other options are not correct because they do not express a wish or desire in the past tense. The verb “would be” is used to express a future possibility or probability. The verb “could be” is used to express a possibility or ability. The verb “had been” is used to express a past action or event that has a bearing on the present.
Here are some examples of how the other options could be used in a sentence:
- I would be taller if I ate more vegetables.
- I could be taller if I wore high heels.
- I had been taller if I had started growing taller earlier.
I hope this helps!