To find if x + y – z + t is even or not, we need to know each of x, y, z, t is even or odd.
It is given that x + y + t is even .... from I
We now just need to check if z is even or odd.
If z is even, then (even - even) will be even. If z is odd, then (even - odd) will be odd.
From II, we can conclude that both t and z are odd as product of two odd numbers is odd.
even - odd = odd
So, we need both the statements to conclude if x + y - z + t is even.
A is the answer.