Step 1: Understanding the Concept
Thermoplastic polymers have linear or slightly branched chains and can be softened repeatedly by heating. Examples are polythene, polystyrene and PVC.
Step 2: Classify the Options
Neoprene is an elastomer, bakelite is a thermosetting polymer, and polythene is a standard thermoplastic. Terylene is a condensation polyester used as a fibre.
Step 3: Compare the options
The textbook thermoplastic in the list is polythene, option (C).
Final Answer:
Polythene is a thermoplastic polymer.
\[ \boxed{\text{(C) }\text{Polythene}} \]