Option 3 is the right answer: and. The conjunction 'and' joins the two things named -- 'price fluctuations' , 'unforeseen emergencies'. The given sentence is about a buffer stock that is kept aside for future different uses. So, the right word is--'and', as it joins the two types of future use. Complete sentence: Buffer stock refers to a reserve of a commodity that is used to offset price fluctuations and unforeseen emergencies.