Concept:
The Sultanganj Buddha is one of the largest surviving ancient bronze (copper) images of the Buddha, discovered at Sultanganj in present-day Bihar. It is a masterpiece of the late Gupta artistic tradition (often dated to the 6\textsuperscript{th}--7\textsuperscript{th} century CE) and is renowned for its graceful modelling, serene expression, and elegant drapery.
The sculpture is made using the lost-wax (cire perdue) casting technique and is presently preserved in the Birmingham Museum and Art Gallery, England.
Step 1: Identify the artistic period of the Sultanganj Buddha.
The Sultanganj Copper Buddha belongs to the
\[
\boxed{\text{Gupta Period}}
\]
and reflects the classical ideals of Gupta art.
Step 2: Examine the given options.
• Gupta Period -- Correct; the Sultanganj Buddha is a masterpiece of the Gupta artistic tradition.
• Kushan Period -- Earlier period associated mainly with Mathura and Gandhara Buddha images.
• Gandhara Period -- Known for Greco-Buddhist stone sculptures, not the Sultanganj bronze.
• Satavahanas Period -- Primarily associated with Amaravati and early Buddhist art.
Hence,
\[
\boxed{\text{(A) Gupta Period}}
\]