Correct Answer:
A. 43
The given series 11, 13, 17, 19, 23, 29, 31, 37, 41 consists of prime numbers in ascending order. A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Following 41, the next prime number is 43. 47 is prime but not next, while 51 and 57 are composite numbers.