Answer:
Correct choice is B
Step-by-step explanation:
The i-th term of the binomial expansion [tex]\left(x-y\right)^{n}[/tex] is
[tex]T_i=C^{n}_{i-1}\cdot \left(x\right)^{n+1-i}\cdot (-y)^{i-1}.[/tex]
For any n, when i=2,
[tex]T_2=C^{n}_{2-1}\cdot x^{n+1-2}\cdot (-y)^{2-1}=-C^{n}_1\cdot x^{n-1}\cdot y.[/tex]
Since [tex]C^{n}_1[/tex] is always positive, then the second term has negative sign.
