Answer: C. insert a comma after 20
Step-by-step explanation:
From the statement given, the comma after example and the comma after states are correct. The mistake in the statement written is that there is no comma after 20.
When writing the date using the month-day-year format, we should note that commas are placed after the day and also after the year.
Therefore, there should be a comma after 20. The right way to write it is April 20, 1998, states, .....