Choose the word whose underlined part is pronounced differently from the others

task1:choos the word whose underlined part is pronounced differently from the others.
1.a.thirsty   b.throw    c.theme    d.there
2.a.breathe   b. fourth   c.tooth   d. warmth
3.a.then   b.thing   c.them   d.their
4.a.birthday   b.mouthful    c.although   d.worth
5.a.everything   b.rthythm   c.healthy   d.nothing