ANSWER
a.
positive
Step-by-step explanation
The given binomial expansion is:
![{(x - y)}^(n)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/m1rht7d37bbptu5a8iicy5qsein046be3d.png)
We can see that the second term is negative (-y).
When we expand this binomial for n=3,4, and 5, the sign is got to alternate.
The first term is positive
The second term negative
The third term is positive
The first choice is correct.