Latin Lesson 10 quiz question

[Joy Shepard 0]

I would like to have some clarification on one of the quiz questions. In Lesson 10 (More on Verb Conjugations) the quiz asks:

"The verb "fero, ferre" is irregular because:

a. It varies its spelling in unpredictable ways

b. It does not end in a vowel as most verbs do. 

I selected "b" but was marked as incorrect.  Can someone explain if "a" would be a better answer, why that is? I thought it was irregular because the stem 'fer' does not end in a vowel as most verb stems do.  

Thanks

[Dianne Williams 0]

I agree Joy.  This looks to me like a 'gotcha' question and it is not the first time there's been such a question. There really is no 'unpredictability' in the spelling because of the 'fer'.  Of course, if the question is referring to the unpredictability of 'tuli' and 'latum', then it should say so as a condition of the question.   I look forward to a defence of 'a' as a better answer, too...