The point …, …, … moves on a space curve

The point $x=\cos t$, $y=\sin t$, $z=t$ moves on a space curve.
(a) In three-dimensional space $(ds{)}^2$ equals $(dx{)}^2+$ ______. In equation (6), $ds$ is now ______ $dt$.
(b) This particular curve has $ds=$ ______. Find its length from $t=0$ to $t=2\pi$.
(c) Describe the curve and its shadow in the $xy$ plane.

Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §8.2 Length of a Plane Curve, #31