"the town of armero, colombia -- buried by mudflows triggered by the 1985 eruption at nevado del ruiz -- was located on a debris fan that was overrun by destructive mudflows in the year 1595, shortly after the arrival of the spanish colonists, and again in 1845, killing hundreds of people in each instance."

which summarizing identifiers are included in this sentence?
a. what, when, where
b. how, what, why
c. when, where, who
d. where, how, why