Concept:For f(x) to be real, ef(x) must be positive.Explanation:Given ex+ef(x)=e, isolate ef(x):ef(x)=e−exSince ef(x)>0 for every real f(x), the right side must also be positive:e−ex>0e>exThe exponential function is strictly increasing, so:1>xx<1At x=1, we get ef(x)=e−e=0, which is impossible because an exponential function is never zero.Hence, x=1 is excluded from the domain.Answer:The domain of f(x) is (−∞,1), so the correct option is B.