Row echelon forms of the augmented matrices for three systems of linear equations in 𝑥 , 𝑦 and 𝑧 are given below. For each augmented matrix, 𝐴 , 𝐵 and 𝐶 , which of the following options correctly describes the number of solutions to the corresponding system of linear equations? [ 1 0 0 | 2 0 1 0 | 0 0 0 1 | − 1 ] ⏟ 𝐴 [ 1 0 0 | − 2 0 0 0 | 0 0 0 0 | 0 ] ⏟ 𝐵 [ 1 0 0 | 0 0 1 0 | 4 0 0 0 | − 2 ] ⏟ 𝐶单项选择题