I think the first question is b and the second is c
B. Where is Susie's bracelet?
You don't need to add the at.
A) This is still a reliable source because it clearly cites scientific research.
A is the correct answer because of the fact that they did the study over several dogs, feeding them the same amount of food, at the same time. They did everything the same, while Anna didn't for her dog.
Hope this helps.
Tone is the way the author or speaker makes their work sound.
