1. Cat's (singular possessive)
2. boss's (singular possessive)
3. elephants' (plural possessive)
I would say, it’s b, ‘what rewards will I get from using this source’
Im 99% sure that is correct as long as you understand the definition of the word implementing you should be able to answer this question. So if i were you i would look in a dictionary for the definiton then decide if it is.
