3. How many of these five expressions give answers which are not prime numbers?
$$
1^{2}+2^{2}
$$
$2^{2}+3^{2}$
$3^{2}+4^{2}$
$4^{2}+5^{2}$
$5^{2}+6^{2}$

A 0
B 1
C 2
D 3
E 4
3. B The values of the five expressions are $5,13,25,41$ and 61 respectively. Of these, only 25 is non-prime.