Verified answer

Answer:

e. 23

Step-by-step explanation:

Note that we can express 19 = 2 + 17, 20 = 3 + 17, 21 = 2 + 19 and 22 = 3 + 19.

Suppose that 23 can be expressed as a sum of two prime numbers, then one must be odd and the other must be an even.

Since the only even prime number is 2, the other number is 21, which is not a prime number, thus, a contradiction.

∴ The answer is e. 23

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