The answer key shows a and b as SN2 reactions and the third as an E2 reaction. How can a primary leaving group go through elimination?
Hey there! I've posted how the structures would look like after each reaction. For C, it would go through E2 since (CH3)3COK is a bulky base and would be sterically hindered to do SN2. This flowchart can really help you with identifying reactions: https://www.clutchprep.com/organic-chemistry/big-daddy-mechanism-flowchart/?c_id=491
I hope this helps!