Teacher:In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Teacher: Now, understand the problem? Solve this instance: This has a mainspring , a spiral of metal ribbon .
Student:
A clockwork mechanism is often powered by a clockwork motor consisting of a mainspring , a spiral torsion spring of metal ribbon .