Take a look at the item again:
When Kate saw the grayish worm on the dissection
tray. (A)
She folded her arms (B)
and refused to pick up the scalpel
(C) even though she would
earn a zero in lab.
You wanted to do this:
When Kate saw the grayish worm on the dissection tray. She folded her
arms. And refused to pick up the scalpel
even though she would earn a zero in lab.
Putting a period after arms will make and refused to pick up the scalpel ... a lonely verb fragment. You need no punctuation between arms and and.
You might want to review the rules.
Go back to the sentence to try again.