Concept:The given sum simplifies using the property 1/i=−i, leading to a geometric series of powers of i.Explanation:Let S=∑n=120(in−1+in+in+1).Factor out in from each term:S=∑n=120in(i1+1+i).Since i1=−i, we have i1+1+i=−i+1+i=1.Thus S=∑n=120in.The powers of i cycle every 4: i,i2=−1,i3=−i,i4=1, and their sum is i+(−1)+(−i)+1=0.From n=1 to 20 there are exactly 20/4=5 complete cycles.Each cycle contributes 0, so S=5×0=0.Answer:0, which corresponds to option B.