For the last two riffs I decided to add some colour tones to the 3rd and 7th (such as the 9th and 13th) to get a more interesting sound.
Note that none of these examples utilize a root note. Root notes are not always necessary when you’re playing along to a bass track. Avoiding root notes can sometimes help prevent the lower register from getting muddy. But keep in mind that there are no rules. Sometimes doubling the root note of the bass player might be just the result you're looking for.
Now, go get to the backing track on the next page and start grooving! :)