Question

In the English language, what is the only verb that doesn't change its spelling regardless of the tense used?

Answer 1

There is more than one such verb.

Explanation:

If you look at the table of irregular verbs you will find verbs like: cost, cut or hurt which have all 3 forms equal.

Another example of such verb is read, but there is a difference in pronounciation of Infinitive compared to Past Simple or Past Participle (the two forms are prononced in the same way).