Question

$47$ 可以用多少种方式写成两个质数的和？

In how many ways can $47$ be written as the sum of two primes?

$0$

$1$

$2$

$3$

多于 $3$

more than $3$

因为 $47$ 是奇数，若两个质数的和等于 $47$ ，其中必有一个偶质数。唯一的偶质数是 $2$ 。

于是另一个数必须是 $47 - 2 = 45$ ，但 $45 = 9 \times 5$ ，不是质数。因此没有这样的表示方式。

所以正确答案是 A。

Since $47$ is odd, a sum of two primes equal to $47$ needs one even prime and one odd prime. The only even prime is $2.$

That would require the other number to be $47 - 2 = 45,$ but $45 = 9 \times 5$ is not prime. So there is no way.

Thus, the correct answer is A .