First, best is a superlative, so the phrase best describes means there's only one answer. Second, if it's a multiple choice test, then there can only be one answer, so there shouldn't be cause for concern over ambiguity. Third, your 3rd example question, provided here below as 2., is a variation of question 1.
1. Which one of the following statements best describes ...
2. Which (one) of the following statments best describes ...
The word one has been omitted in 2., and omitting it doesn't change the meaning of the sentence.
Lastly, clarity is everything, especially on an exam. If you suspect that ESL students might think question 2. is ambiguous, then don't use it. If, however, it was already written on an exam, and the result was that the test takers provided more than one answer, then they were wrong in doing so. The reason being, it was a multiple choice test. Only one answer is correct. Right?
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