Vector Projections: Same Projection onto XY Plane?

[waters]

Which of the following curves have the same projection onto the xy plane?
a) <t, t^2, e^t>
b) <e^t, t^2, t>
c) <t, t^2, cost>

 

[Spinnor]

Projecting onto the xy plane means setting z = 0 ?

 

[waters]

I don't know, but that makes sense.