Pick out the word that has different stressed syllables from the others

Question 1: Pick out the word that has different stressed syllables from the others:
1.A. convenient
B. dificuit
C. historic
D.exciting
2.A. valley
B.fantastic
C.polluted
D.expensive
Question 2:Choose the best words to fill in the blank:
1. You ....... travel alone on the mountain. You......... always go in group.
A.must/ mustn't B.mustn't/ must C.can/ must D. can't/ can
2. A bicycle is often more......... than a car.
A. faster B. cheaper C. more convenient D. more expensive