Which of the following statements about irregular verbs is correct?

Although none of these are completely correct, I'd choose D. to change tenses, an irregular verb has to change its spelling.

A is definitely incorrect - that is a rule about regular, rather than irregular verbs. B is also incorrect - there are no rules about irregular verbs so you have to learn them all by heart. C is incorrect because this is true for regular verbs as well, not just irregular.

This leaves us with D as the correct answer. Often, various forms of irregular verbs change more or less drastically. For example: see - saw - seen; ring - rang - rung, etc.

To change tenses, an irregular verb has to change its spelling. An irregular verb is in past tense, but does not end in ed or - d. (example: feel as an irregular verb changes its spelling to "felt")