What does a positive part-worth utility estimate for a specific attribute level in a conjoint analysis suggest?

a) The attribute level is not relevant for decision-making because we have no way of calculating p-value.

b) We can't tell whether the attribute level has an impact on respondents' preferences unless we know the p-value.

c) Respondents prefer that attribute level over the reference level.

d) Respondents dislike that attribute level compared to the reference level.