What are the expected phenotypes of the offspring?

Farmers who raise sheep for wool try not to produce offspring with black wool. Black wool is very brittle and difficult to dye; therefore, white wool is more desirable. If a farmer purchases a white ram, he will generally carry out a test cross to determine whether the ram is heterozygous or homozygous for white wool. White wool (W) is dominant to black wool (w).
If the ram is heterozygous for white wool, the expected phenotypes of the offspring of the farmers test cross would be

A. all white
B. 1/2 black and 1/2 white
C. 3/4 black and 1/4 white
D. all black

I know it has to be A or B but I couldn't figure it out, could you explain please?