Final answer:
A macro conversion for an ecommerce site is represented by a completed sales transaction, which directly impacts the site's revenue and marks a definitive measure of success.
Step-by-step explanation:
The question revolves around the concept of macro conversions within the context of an ecommerce platform. In this scenario, a macro conversion refers to a key action that contributes directly to the primary objective of the site, often related to revenue generation. Here, the answer to our inquiry would be b) a completed sales transaction. This option directly affects the revenue of the ecommerce site and is a definitive measure of its success.
Other options like receiving a product inquiry, collecting a lead, or a click on a "buy" button, while important parts of the conversion funnel, do not represent the actual completion of a sale. These are considered micro conversions which are more about engagement or steps towards a potential sale rather than the sale itself.