Final answer:
The correct option for expressing Kate's opinion on the shoes is 'I prefer the ones you tried on first' because it accurately reflects her current preference in simple present tense.
Step-by-step explanation:
The correct response to Jill's question "What do you think of these shoes?" given the options would be a) I prefer the ones you tried on first. This is the correct form of expressing a preference in simple present tense, which is the tense used by Kate in her response. Option b) is incorrect because 'prefer' is not typically used in the continuous form. Option c) is incorrect because 'am preferred' is a passive construction that does not fit the context of expressing an opinion. Option d) suggests future preference, which is also incorrect for expressing a current opinion.