Here are the words where the underlined part is pronounced differently:

1. **C. dancing** (the "an" sound is pronounced differently from "class," "fast," and other options)
2. **C. notebook** (the "oo" sound is pronounced differently from "brother," "lovely," and others)
3. **C. above** (the "ove" sound is pronounced differently from "love," "start," and others)
4. **C. start** (the "ar" sound is pronounced differently from "smart," "dollar," and others)
5. **C. understand** (the "un" sound is pronounced differently from "study," "computer," and others)

So the answers are:
1. C
2. C
3. C
4. C
5. C