A crescendo of metallic thuds arose from the market, where the iron-smiths were …… the pieces of metals. A. flattening B. striking C. hammering D. thrashing

The correct answer is C. hammering.

Flattening is the process of making something flat, while striking is the act of hitting something with force. Hammering is the act of hitting something with a hammer, which is a tool that is used to shape or break objects. Thrashing is the act of hitting or beating something violently.

In the context of the question, the iron-smiths are using hammers to shape the pieces of metal. This process is called hammering.