The main difference is that a monk remains within his community while the friar has a public ministry. Generally speaking, once a monk enters the cloistered life, he does not leave. Friars are often given assignments in the world although they do have a communal life. This is why friars such as the Franciscans and Dominicans were very active in the evangelization of the New World while monks like the Benedictines established monasteries much later.
The correct options are B AND D.
Agriculture was the major means of survival for men during the early days. Fluctuations in the rainfall during the course of a year may adversely affect the crops grown. If this persists for a long time it will leads to food shortage and famine.
Earthquake and eruption volcanoes are shift in the physical environment which can easily destroy any community.
I think d if you still need the answer
The extension of slavery into the western territories.
For a specific instance, see the landmark supreme court case Dred Scott v. Sandford.
