Two numbers a and b are such that one is odd and the other is even. Which statement is necessarily true?

Prove that the sum of two odd numbers is even.

Prove that the sum of two odd numbers is even.

Prove that the sum of two odd numbers is even.

Prove that the sum of two odd numbers is even.

Prove that the sum of two odd numbers is even.

If a and b are two integers which are multiples of 5 which of the following is not necessarily true :

If a, b, c and d are four positive real numbers such that sum of a, b and c is even the sum of b,c and d is odd, then a^2-d^2 is necessarily

If a and b are two different positive real numbers then which of the following statement is true?