Before ____________of synthetic dyes, yarns were often colored by dyes obtained from natural vegetable and mineral matter.

Before ____of<br/>synthetic dyes, yarns were often colored by dyes obtained from<br/>natural vegetable and mineral matter. A: introducing B: introduction C: the introduction D: introducing that

The<br/>spinning process of combing pure cotton is followed by cotton<br/>assorting, cleaning and carding,(),<br/>()<br/>drawing 1~2<br/>passes, roving, () and finishing, to form the the desired cotton<br/>yarns or threads. A: Preparation for combing B: Combing C: Roving D: Spinning