As it says he keeps 'pairs' of shoes so the answer has to be an even 'number' - ie B, C and E are all possible answers.
Answer:
Imperfect substitutes
explanation:
The choices above are not perfect substitutes, meaning they can not be perfectly or directly replace the other. Imperfect substitutes are close substitutes but not perfect substitutes. Unlike perfect substitutes, imperfect substitutes satisfies same utility but has different characteristics and therefore not entirely substitutable. For example, while one may want to have the 40 marks too, he'd rather have 60 marks even if the criteria for a 60 mark score was increasingly hard.
