Here are the answers to the exercises you've provided:

**Exercise 3: Different Sound**
The word with a different sound in the underlined part is:
- 1. A. knock (different sound: the "o" in "knock" is short /ɒ/ while the others have different vowel sounds).

**Exercise 4: Different Stress**
The word which has different stress from the others is:
- 1. A. costume (it is stressed on the first syllable, whereas others like "diverse," "livestock," and "pharmacy" have varying stress patterns).

Let me know if you need further assistance!