I think this question asks which combination is correct. Because looking at it alone, ① ② ③ cannot be deduced, which means that A and B are wrong. If x is odd and y is odd, then x+y is even and x*(x+y) is even, so c is wrong. If y and x+y are odd numbers, then x is even, and x*(x+y) is even, then e is wrong and there is only X.
2. How many possibilities does n have to make the value of (2n+ 1) (3n- 1) negative?
This problem is to solve inequalities. According to the meaning of the question,
Either 2n+1; 0
Either: 2n+1>; 0 and 3n- 1
The conclusion of the first set of inequalities is that there is no N < (n; 1/3)
The conclusion of the second set of inequalities is-1/2.