Joseph got their homework done with ease while Leslie kept running into obstacles, so 
OPTIONS:
- Joseph took a long time to get theirs done.
- Leslie took a long time to get theirs done.
Leslie took a long time to get theirs done.

The trudge through the forest was a task, but they climbed the mountain painlessly, since the 
OPTIONS:
- forest was a pleasant environment.
- mountain was a pleasant environment.
mountain was a pleasant environment.

As soon as the sun came out Megan wanted a popsicle while Amy preferred froyo. 
OPTIONS:
- Megan was lactose intolerant.
- Amy was lactose intolerant.
Megan was lactose intolerant.