A “Sophie Germain” prime is any positive prime number p for which 2p + 1 is also prime. The product of all the possible units digits of Sophie Germain primes greater than 5 is
Choose the correct choice from the following answers.
A) 3	B) 7	C) 21	D) 27	E) 189
A prime number greater than 5 can have only the following four units digits: 1, 3, 7, or 9.   If the units digit of p is 1 then the units digit of 2p+1 would be 3, which is a possible units digit for a prime. For example consider p=11=prime --&gt; 2p+1=23=prime;   If the units digit of p is 3 then the units digit of 2p+1 would be 7, which is a possible units digit for a prime. For example consider p=23=prime --&gt; 2p+1=47=prime;   If the units digit of p is 7 then the units digit of 2p+1 would be 5, which is NOT a possible units digit for a prime;   If the units digit of p is 9 then the units digit of 2p+1 would be 9, which is a possible units digit for a prime. For example consider p=29=prime --&gt; 2p+1=59=prime.   The product of all the possible units digits of Sophie Germain primes greater than 5 is  1*3*9= 
<gadget id="calculator"> 1*3*9</gadget>
<output>27</output>
27.   Answer: 27.
<result>D</result>
A “Sophie Germain” prime is any positive prime number p for which 2p + 1 is also prime. The product of all the possible units digits of Sophie Germain primes greater than 5 is