Problem: How does the sentence end?

the toxic chemicals corroded the walls of the pipes rapidly , the 
Answer: chemicals were strong.

Problem: How does the sentence end?

The doctor had to give the old patient steroids instead of the hormones because the 
Answer: hormones were not working.

Problem: How does the sentence end?

Rebecca was instructing Katrina on how to ski because 
Answer: Katrina was a student on the mountain.

Problem: How does the sentence end?

Steven grew up in a poorer neighborhood than Jeffrey, so 
Answer:
Jeffrey was unaware of not feeling safe in the dark.