Answer:
D. the estimated average of Y increases by 2 units for each increase of 1 unit of X1, without regard to X2.
Explanation:
Hello!
Given any linear or multiple regression, βi represents the modification on the population mean of Y when Xi increases one unit. And its estimator bi is defined as the modification on the estimated mean of Y when Xi increases one unit.
So if you have an estimated multiple regression model Yi= b₀ + b₁X₁ + b₂X₂ + ... + bkXk
Where k is the number of regressive variables.
b₁ is the modification of the estimated average of Y when X₁ increases one unit and the rest of the independent variables remain constant.
In other words, the estimated mean of Y increases 2 for each unit increase of X₁.
I hope it helps!