The Variance of the Slope in a Regression Model

In my "applied linear models" exam, there was a tricky question (it was a multiple choice, so no details were asked). I was simply asking if the following statement was valid, or not

Consider a linear regression with one single covariate, y=β0+β1x1+ε and the least-square estimates. The variance of the slope is Var[β1] Do we decrease this variance if we add one variable, and consider y=β0+β1x1+β2x2+ε ?