Problem: How does the sentence end?

the toxic chemicals corroded the walls of the pipes rapidly , the 
OPTIONS:
- walls were strong.
- chemicals were strong.
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 
OPTIONS:
- steroids were not working.
- hormones were not working.
Answer: hormones were not working.

Problem: How does the sentence end?

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

Problem: How does the sentence end?

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