C. plumber (The "b" is silent, unlike the other words where the "b" is pronounced.)

D. junkyard (The "u" is pronounced differently, as "ʌ" in "junkyard", compared to the other words where "u" is pronounced as "ɜː" or "ʌ".)

D. respond (The "re" is pronounced as "rɪ", while the others are pronounced with "ɪ" or "æ".)

B. costly (The "o" in "costly" is pronounced differently compared to the other words where the "o" is pronounced like /əʊ/.)

D. stomach (The "t" in "stomach" is pronounced differently from the "ch" in the other words, where it has a "tʃ" sound.)