Selected answer is INCORRECT, which is corrct?

If I have the following model: 33c = be + blmsl + 523a The correct way to interpret b1 is: The model predicts that a one unit increase in x1 is associated with a bl change in y, on average. holding x2 constant. (0': The model predicts that a one unit increase in x1 is associated with a bi change in y, on average, only among observations where x2 is zero. All ofthese. The model predicts that a one unit increase in x1 is associated with a bl change in 3;, on average