Find the unit tangent vector t(t) at the point with the given value of the parameter t.
r(t)=√4t​i−2t²j+4tk, t=1.
a. t(1)= i/2 - 2j - k
b. t(1)= i/2 - j + 2k
c. t(1)=2i - 2j +k/2
d. t(1)=i/2 - j +k/2