In building construction, which of the following could potentially contain lead?

In building construction, all of the mentioned options could potentially contain lead.

Electrical fittings may contain lead in their solder used for connections or in the materials themselves that were manufactured before regulations restricted lead use. Lead solder was commonly used in electrical work due to its favorable properties for creating durable connections.

Plumbing fixtures, particularly older ones, might also contain lead, especially in their soldered joints and in the brass used to manufacture many components. Historically, lead was often used in piping systems, which could pose health risks if lead leaches into drinking water.

Special sheetrock used for X-Ray labs is specifically designed to provide radiation shielding, often incorporating lead within its composition to prevent radiation from passing through. This type of sheetrock is a critical safety feature in medical environments but inherently involves lead as part of its structure.

Each of these items points to the potential for lead presence, thereby justifying "All of these" as the correct answer. Understanding the contexts in which lead can exist is crucial for safety, regulatory compliance, and health considerations in construction and renovation projects.