Final answer:
The Pantheon was completed last, under Emperor Hadrian's reign, between 125 and 128 CE, following the initiation of its construction by Trajan.
Step-by-step explanation:
The student has asked which of these historical structures was built last: the House of the Tragic Poet, the Forum of Augustus, the Pantheon, or the Sanctuary of Fortuna Primigenia. By examining historical records, we find that the Pantheon, as it stands today, was completed under Emperor Hadrian. Although initiated by Trajan, the majority of its construction took place during Hadrian's reign, between 125 and 128 CE, making it the last of the mentioned buildings to be completed. The Pantheon was built last among the options given: House of the Tragic Poet, Forum of Augustus, Pantheon, and Sanctuary of Fortuna Primigenia.
The Pantheon was initially built by Agrippa in 31 BCE but was damaged by fire and restored by Emperor Domitian.
However, a reconsideration of the evidence suggests that the Pantheon as we know it today was substantially designed and rebuilt under the reign of Emperor Trajan, finishing sometime between 125 and 128 CE.