Let's analyze the pronunciation and stress of the given words:
Pronunciation
Question 1:

A. painless: /ˈpeɪnləs/
B. envious: /ˈɛnvɪəs/
C. upset: /ʌpˈsɛt/
D. tennis: /ˈtɛnɪs/
Analysis: The underlined vowel sound is different in C. upset. It has a short vowel sound (/ʌ/), while the others have a long vowel sound (/eɪ/).

Answer: C. upset

Question 2:

A. background: /ˈbækɡraʊnd/
B. paddle: /ˈpædl/
C. tragic: /ˈtrædʒɪk/
D. starving: /ˈstɑːvɪŋ/
Analysis: The underlined consonant sound is different in D. starving. It has a voiced /v/ sound, while the others have a voiceless /p/ sound.

Answer: D. starving

Stress
Question 3:

A. skateboarding: /ˈskeɪtbɔːrdɪŋ/
B. delighted: /dɪˈlaɪtɪd/
C. injury: /ˈɪndʒərɪ/
D. waistcoat: /ˈweɪstkəʊt/
Analysis: The primary stress is on the first syllable in A. skateboarding. In the other words, it's on the second syllable.

Answer: A. skateboarding

Question 4:

A. excite: /ɪkˈsaɪt/
B. confusing: /kənˈfjuːzɪŋ/
C. frightened: /ˈfraɪtənd/
D. embarrass: /ɪmˈbærəs/
Analysis: The primary stress is on the second syllable in B. confusing. In the other words, it's on the first syllable.