The table below shows information about four different substances.
| Substance | Melting point (∘C^{\circ}\text{C}∘C) | Appearance | Electrical conductor? |
|---|---|---|---|
| W | 660660660 | shiny solid | yes |
| X | 801801801 | white crystalline solid | yes when dissolved in water |
| Y | 130130130 | flexible solid | no |
| Z | 444444 | waxy solid | no |
Which of the substances is a polymer? Explain your answer.
Explain why polymers without cross-links can stretch and flex much more than polymers with cross-links.

Which substances from the table would be best to use to make each part of the pliers? Explain your answers.
Part A (outer handle grip):
Part B (metal jaw):