Question

A main provision of the Monroe Doctrine was to: encourage American involvement in European affairs prevent European interference in North and South America enable Spain to control colonies in the hemisphere

Answer 1

A main provision of the Monroe Doctrine was to "prevent European interference in North and South America", since many in the US saw this as a threat to national security. 

Answer 2

The correct answer is: "prevent European interference in North and South America"

The Monroe Doctrine was issued in 1823 as a mechanism of opposition to  European colonialism. In that moment, most former Latin American Spanish and Portuguese colonies had gained independence of were about to do it.

It stated that any actions undertaken by European countries aiming to exercise dominance over any American territories would be regarded by the US "as the manifestation of an unfriendly disposition towards the United States", acting in consequence.