What were some explanations as to why the age of exploration began in 1492?

The reason for that is the Silk Road, where all the prices as an item was passed from merchant/seller to merchant/seller the price would increase. By the time it reached the Europeans/Spaniards only the rich people could afford it. Thus they needed to find a way to Asia for silk as well as spices.  

in 1803 the louisiana purchase took place, doubling the size of the country. by 1840 almost 7 million americans had migrated westward in hopes of securing land and being prosperous. the belief that settlers were destined to expand to the west is often referred to as manifest destiny.

explanation:

i believe the answer to your question is b. pay your bills early