Titus was the second emperor of the Flavian Dynasty. Although he ruled briefly, from 79 to 81 CE, his rule is important because it coincided with the eruption of Mount Vesuvius and a terrible fire in Rome. Titus was remembered fondly by the Romans for leading the disaster relief campaign in the wake of these two catastrophes.

Nero blamed the fire on the Christians. This initiated the persecution of the Christians under his reign. This question is tricky because your first instinct is to choose the Ottomans. Remember that the Ottomans didn't invade under Nero's rule. We can also rule out the Atheists and the Jewish options, because these were not prevalent in the Roman empire at the time. 

Vespasian was the first emperor of the Flavian Dynasty; he took power in 69 CE and ruled until his death in 79 CE. Titus was Vespasian's eldest son and succeeded Vespasian after his death, ruling for just two years before his death from an unknown illness.

All three of these natural disasters befell the Roman Empire in extremely short order in Titus first year of rule (79 CE). The devastation wrought on Pompeii and surrounding regions following the eruption of Mt. Vesuvius was immediately followed by a large, devastating fire in Rome and a plague in the aftermath of the fire.

Vespasian's rule marked the beginning of the Flavian dynasty, at the end of a year during which three other emperors previously ruled (Galba, Otho, and Vitellius). Before them, Nero had been emperor. As such, the other answers are incorrect.

The eruption of Mt. Vesuvius in 79 CE, destroyed the two Roman cities of Pompeii and Herculaneum, burying the two cities underneath dozens of feet of ash and killing thousands of people.

It remains as one of the most deadly volcanic eruptions in world history.

The Roman Coliseum, also called the Flavian Amphitheatre, was built during the reign of Emperor Vespasian and was finally completed shortly after Vespasian died (during the reign of Emperor Titus, Vespasian’s son). The Coliseum was used to stage gladiatorial battles and other public exhibitions.

The key to this question is the transition from the Julio-Claudian dynasty into the Flavian dynasty. As power shifted from the senate/militia into imperial power, four main emperors fought this war to gain ownership of the throne. Caesar ruled the dynasty before, the Marian Sullan war represents the first civil war in Roman history, and the other three options were fought in the common era- long after the Julio Claudian dynasty ended

The Flavian Dynasty ruled from 69 CE to 96 CE. It began with the rule of Vespasian, who took power during the turbulent period known as the Year of Four Emperors. Vespasian was succeeded by his son Titus, who ruled for two years, before himself being succeeded by Domitian. Domitian ruled for fifteen years before he was assassinated on the orders of the Senate.

The Nerva-Antonine Dynasty ruled the Roman Empire from 96 to 192 CE. After the fall of the Nerva-Antonine Dynasty, the Roman Empire entered into a turbulent period known as the Year of the Five Emperors. This civil war was eventually ended when Septimius Severus took power and founded the Severan Dynasty.