Consider the population regression of log earnings (y, where y= in(earnings)l against two binary variables: whether a worker is married (d1 where d1= 1 if the person is married) and the worker's gender where(d2,where d2=1 if the person is female), and the product of the two binary variables y= β0+1d1+β2d2+β3(d1xd2) + μ. the interaction word (d1 x d2)a) allows the population effect on log earnings of being married to depend on gender b) does not make sense since it could be zero for married males c) indicates the effect of being married on log earnings d) cannot be estimated without the presence of a continuous variable