For which kkk is the determinant of (k21k−1)\begin{pmatrix} k & 2 \\ 1 & k-1 \end{pmatrix}(k12k−1) equal to 000?
2,−12, -12,−1
1,−21, -21,−2
2,12, 12,1
−1,−2-1, -2−1,−2