You have the following expression:
3x - 1
and the following statements about the previous exprassion.
A. the difference of one and three times a number
B. one less than three times a number
C. thrice a number, minus one
D. one subtracted from three times a number
From the previous sentence, B is NOT a way to express the given algebraic expression, because in this sentence the algebraic expression is:
1 - 3x
The rest of options express corectly the given expression 3x - 1.