premise: An industrial electrician attaches exactly seven components designated S, T, V, W, X, Y, and Z to a circuit board in exactly seven consecutive steps; exactly one component is attached per step. Each component is attached exactly once, and each is attached either by hand or by machine, but not both. X is the fourth component attached. Exactly two components are attached by hand at some time before X is attached. No component is attached by hand before T is attached. W is attached at some time before T. Y is attached at some time after both Z and S. The sixth component attached is attached by hand. If S is attached by machine, which one of the following must be true?
hypothesis: Z is attached by hand.