Scientists have described about how many species?

Toward the end of the roman empire, what caused a decrease in the use of coined money tell me now

Countries that are neither core nations nor peripheral nations

Around the third week of a college class, a professor decides she’s had enough, is tired of dealing with bureaucracies, and wants out. so one day, instead of coming to class, she flies to tahiti and sells souvenirs on the beach. if this happened, the college would simply assign a substitute to finish the course. what does this tell you about the nature of the authority wielded by a professor?