as usual, we will consider the pronunciations for all the given options above and choose the one with a differnt sound. 

pass goes thus: [pɑːs]

clerk  [klɑːk]

earth  [əːθ]

lass  [las]

man   [man]

The answer is B because the word ‘pass’ is transcribes /pa:s/ and is a longer form of /ae/. In the options above the word ‘earth’ /Ʒ:o/ or /Ʒ or o/, ‘lass’ /wes/ but the word ‘clerk’/kla:k/ has the same long vowel sound as pass /pa:s/