I think this demonstrates the difficulty of setting 'odd one out' puzzles. opsoccergurl11 is right about question 2 (though I had another answer in mind) RC and piderman are both right about question 3.
Re number 1
As "teach, sing, bring, seek" the odd one out is "teach" because its the only word that doesn't make a new word if you add "s" to the end.
If left as "teach, sing, bring, preach" the odd one out is "bring", because its the only word that is not an occupation if you add "er" to the end.