A batch of industrial components contains 5 'Grade-A' units, 1 'Grade-B' unit, and 1 'Grade-C' unit. A quality control officer selects two units at random, one after the other, without replacement.
Construct a tree diagram to represent all possible outcomes of this selection process, including the probabilities for each branch.
Determine the probability that the officer selects exactly one Grade-B unit and exactly one Grade-C unit.
