Final answer:
The last structure built among the Forum of Augustus, Sanctuary of Fortuna Primigenia, Pantheon, and House of the Tragic Poet was the Pantheon, reconstructed around 125 CE under Emperor Hadrian.
Step-by-step explanation:
The question pertains to the chronological order in which certain Roman structures were built. Among the structures listed—the Forum of Augustus, Sanctuary of Fortuna Primigenia, Pantheon, House of the Tragic Poet—the last to be built was the Pantheon. The Sanctuary of Fortuna Primigenia was constructed in the 2nd century BCE, and the Forum of Augustus dates back to the reign of Emperor Augustus. The Pantheon, as we know it today, was rebuilt by Emperor Hadrian around 125 CE, after a prior iteration was damaged.
The House of the Tragic Poet, in Pompeii, is estimated to date back to the 2nd century BCE, but considering the question refers to more prominent public buildings and the Pantheon's substantial construction under Hadrian, the Pantheon is likely the structure of interest. As a result, based on the available data, the Pantheon was constructed after the other buildings mentioned.