What does a composer do when orchestrating a piece of music? assigns different musical lines to different instruments in a piece of music sequences themes into a composition adapts a piece of music for different instruments creates movements for a symphony?

For different instruments the composer will assign different musical lines consisting of notes. Subsequently, he/she will combine them to produce a piece of music that sounds good to the ear. The composer may also take already composed music and assign different lines of music to different instruments, thereby putting his own ideas and thoughts into the piece.