All prime numbers are odd except 2 so,

odd+odd=even

even+odd=odd

so, check for 19 it is 2+17=19(both 2 & 17 are prime)

check for 45 it is 2+43=45 (both 2& 43 are prime)

check for 68 as it is even so both prime number if applicable should be odd 61+7=68 (both 61 & 7 are prime)

check for 79 as it is an odd number it means one of the prime number should be even i.e. 2+77=79 but 77 is not prime so Ans is 79-----(D)

Check for 88 (even) means both prime number should be odd i.e. 83+5=88(both 5 & 83 are prime)

Ans is (D)