The correct options are: "historical events - new ideas - contact with other cultures - social reform"
In the linguistic change we call external causes those that are motivated by sociolinguistic factors related to the history of the speakers of the language, such as their contacts with other people of other languages, the demographic factors and their cultural influences.
Thus, the massive existence of bilingualism in a human group, or the massive presence of loans from one language to another for reasons of technological, religious or cultural influence, has been supposed to provoke linguistic change. For example, the substrate theory, now discarded, was popular for some time, for which the main cause of the differentiation of Latin was that its speakers before Romanization spoke different languages and by transferring part of those features to the Latin they spoke they provoked the fragmentation. In the same type of ideas are based the influences of the superstrate (languages with native speakers in a terrorist that do not become the majority language of the speakers of the territory) over and of the adstrato (set of languages of adjacent territories).
