I need help with this problem please, and please make it legible.

Find the curve's unit tangent vector. Also, find the length of the indicated portion of the curve. r(t) = (5cost)i + (5sin t)j + (13t)k, Osts Choose the correct answer for the unit tangent vector of r(t). 51/7 O A. T(t) = 51/7 121 14 sin ti + 14 cost j + k 14 517 O B. T(t) = sint i+ 51/7 121 14 14 cost j + 14 O C. T(t) = 51/7 517 sint i - V21 14 14 cost j + k 14 O D. T(t) = 517 517 sint i - 121 14 14 cost j + 14 k The length of the curve is . (Type an exact answer, using it as needed.)