Problem: Continue the following story.

Jeffrey fed their guinea pig alfalfa, while Robert fearfully watched from a distance. 
Here's how I want to continue it: Robert was scared of guinea pigs.

Problem: Continue the following story.

The bestselling book was written by Angela and the failing book was written by Betty, because 
Here's how I want to continue it: Betty was a substandard writer.

Problem: Continue the following story.

Maria liked to freehand her posters while Lindsey preferred to be more precise. 
Here's how I want to continue it:
Lindsey always used a ruler.