Answer :
Think of it this way: your friend is thinking of a year, and you have to guess which. She has told you the year is in the 20th century (1900s).
There are 100 years in the 20th century (1901-1999 plus 1900).
There can be 100 possibilities
There are 100 years in the 20th century (1901-1999 plus 1900).
There can be 100 possibilities
100 combinations can be formed from the last two digits. So the answer is (c).