Which of the following experssions has magnitude unity.
A. `(vec(a)+vec(b))/(|vec(a)+vec(b)|)`
B. `|hat(a)+hat(b)|` when angle between `vec(a)`and `vec(b)` is `120^(@)`
C. `(vec(a)-vec(b))/(|vec(a)-vec(b)|)`
D. `|hat(a)-hat(b)|` when angle between `vec(a)` and `vec(b)` is `60^(@)`
