What is given to us is x and y are integers. Also, (x-1)*(y+3)*(xy+3) = 0
This would mean that either of the three terms can be zero,
Thus,
x-1 = 0 ==> x = 1_____ (1)
OR
y+3 = 0 ==> y = -3______(2)
OR
xy+3 = 0 ==> xy = -3 ==> (x = 1, y = -3) OR (x = -1, y = 3) OR (x = 3, y = -1) OR (x = -3, y = 1)_____(3)
Now lets go to the statements. Since it is a must be true problem, if we are able to prove any of the statements wrong for atleast one case, we can eliminate that statement.
Statement (I): If x = -1, |y| is a prime number.
Let's substitute x = -1 in the above eqn:
(-1 - 1)(y+3)((-1)*y + 3) = 0
Thus, (-2)(y+3)(3-y) = 0
We can clearly see from above that,
y+3 = 0 ==> y = -3
OR
3-y = 0 ==> y = 3
Thus, |y| = |3| or |-3| = 3 which is prime.
Hence, Statement (I) must be true.
Statement (II): If, |y| is not prime then x is not prime
From the above (3), let's consider the case y = -1 (since we want |y| to not be prime)
Thus, the eqn becomes,
(x-1)(-1+3)(-1*x+3) = 0
Thus, we know either
x-1 = 0 ===> x=1
OR
-x+3 = 0 ===> x=3
We can see that in the scenario of x=3, x becomes prime. Thus we have a case where Statement (II) is not true. Hence, we can eliminate this statement.
Statement (III): If x is a prime number, y/x is not an integer
From the above (3), let's choose x = 3 (since we want x to be prime)
Thus, the eqn becomes,
(3+1)(y+3)(3y+3)=0
Thus, either y+3 = 0 ==> y = -3 ==> y/x = -3/3 = -1 (an integer)
OR
3y+3 = 0 ==> y = -1 ==> y/x = -1/3
Since we get atleast one case where y/x is an integer, we can eliminate this statement.
Hence (A) is the correct choice here.