Here is the link to Lesson 9 of the Interactive Rimsky-Korsakov Principles of Orchestration:
In this lesson we will begin our discussion on "melody in the different groups of instruments combined." In previous lessons we discussed melody in each of the vaious instrument groups and in this lession we will focus on inter-group combinations. There are interactive scores and many exercises in this lesson.
Here's the link to the course itself:
17 Lessons left to go!
Your participation and involvement is most welcomed.
"The right music played by the right instruments at the right time in the right combination: that's good orchestration." --Leonard Bernstein