If a and b are two-digit positive numbers and c is a three digit positive number, such that c=a+b, is the unit digit of the same as the unit digit of a?

1) All the digits of C are the same and all the digits of a are the same

2) The tens digit of a is the same as the tens digit of b

What's the best way to determine whether statement 1 is sufficient? Can any experts help?