To start or stop the current in a circuit, Keisha should use a switch. In circuit diagrams, switches are often represented by specific symbols. Based on your description, if we assume "W" refers to two separate points close together that might represent a switch, then she should use "W."
If the labels correspond to standard components:
- "X" could represent a battery or power source.
- "Y" could represent resistors or other components, possibly capacitors depending on the representation.
- "Z" usually denotes a connection or wire, sometimes representing ground.
However, without seeing the actual symbols, the best assumption according to your description is that Keisha should use W to start or stop the current.