I need help with this ASAP .. I don't understand it .... For each of the following sentences add commas where they belong. On the line before the sentence, write C if the sentence is correct.

Answer:
6. C
it was thought that aristocrats got sick and died after eating them
7. C
Hindu-Arabic numerals, set of 10 symbols—1, 2, 3, 4, 5, 6, 7, 8, 9, 0—that represent numbers in the decimal number system.
8. not correct.
9. not correct.
10. C
Explanation:
Hope this helps