Problem: Continue the following story.

James believes he could get the same number of grams  of stones with equal volume of oil but he was wrong because the 
Here's how I want to continue it: oil is lighter.

Problem: Continue the following story.

Tim needed to rake the yard underneath the tree because the 
Here's how I want to continue it: tree had dropped its leaves.

Problem: Continue the following story.

The gym trainer was teaching everybody how to get bigger arms before legs, since the 
Here's how I want to continue it:
legs are stronger.