Problem: How does the sentence end?

The baby slept better in the crib by themselves than in the bed with their mother because there was less movement on the 
OPTIONS:
- crib mattress.
- bed mattress.
Answer: crib mattress.
sentence: It took James all the days of the month to finish the paintings because the  OPTIONS:
- days are short.
- paintings are short.
complete: days are short.
I hired a tutor and my brother went to extra classes. He ended up getting better grades than me so the 
OPTIONS:
- extra classes must be pretty ineffective.
- tutor must be pretty ineffective.
tutor must be pretty ineffective.
Input: Continue writing.

Aaron wore the jewelry that Brett had given them, and 
OPTIONS:
- Aaron loved to purchase it.
- Brett loved to purchase it.

Continued: Brett loved to purchase it.
Story needs to be completed:
The cattle at the farm of Angela were thinner than the ones raised by Mary because 
OPTIONS:
- Angela fed theirs more.
- Mary fed theirs more.

My choice:
Mary fed theirs more.
Problem: How does the sentence end?

The rock was worth more money than the stone, because the 
OPTIONS:
- rock was more rare.
- stone was more rare.
Answer:
rock was more rare.