How do paragraphs 17 and 18 of "Wangari Maathai's Nobel Lecture" mainly help develop the central idea?

How did trade contribute to the spread of the plague in the 1300s? trading vessels from the americas brought the plague to london, where it spread across europe. trading caravans from mongolia brought the plague to rome, where it spread across europe. trading caravans from russia brought the plague to barcelona, where it spread across europe. trading vessels from china brought the plague to sicily, where it spread across europe.