Question

Consider a 4-digit number of the form abbb, i.e., the first digit is a (a > 0) and the last three digits are all b.
Which of the following conditions is both NECESSARY and SUFFICIENT to ensure that the 4- digit number is divisible by a?

• A. b is divisible by a
• B. b is equal to 0
• C. 21b is divisible by a
• D. 9b is divisible by a
• E. 3b is divisible by a