Which one of the following is a prime number ?

Answer: Option C

$$\sqrt{437}>20$$
All prime numbers less than 20 are 2, 3, 5, 7, 11, 13, 17, 19.
161 is divisible by 7, 221 is divisible by 13 and 437 is divisible by 19.
373 is not divisible by any of the above prime numbers.
∴ 373 is prime.