Here are the words with a different sound in the underlined part:

1. **C. allergy** - The "a" in "allergy" sounds different (like "æ" as in "cat") compared to the "a" sounds in the other words (like "ey" in "coordinate," "triathlon," and "calorie").

2. **D. of** - The "f" sound in "of" is different from the "f" in "leaf," "life," and "knife," which all have a hard "f" sound.

3. **C. compound** - The "o" in "compound" is pronounced differently than the "o" sounds in "monopoly," "melody," and "concentrate" (which have the long "o" sound, as in "go").

4. **A. paragraph** - The "ph" in "paragraph" produces an "f" sound, while "cough," "although," and "enough" produce different "gh" sounds.

5. **C. essential** - The "e" in "essential" has a different vowel sound compared to the "e" in "vegetarian," "depression," and "attention," which all have a long "e" sound.

So, the words with different sounds in the underlined part are:

1. C. allergy
2. D. of
3. C. compound
4. A. paragraph
5. C. essential