Which of the following pairs of words are minimal pairs based on vowel contrast?

'Bit' /bɪt/ and 'beat' /biːt/ differ only in the vowel sound — the short /ɪ/ versus the long /iː/ — making them a minimal pair based on vowel contrast. Option A differs in the final consonant, option C adds an extra consonant, and option D, while a vowel contrast, changes more than one phonetic feature perceptibly in connected speech context.