4. The concept of encouraging learners to master two languages, we call bilingualism. If learners obtain more than two languages at school or by direct experiences without attending the language classes offered in a particular school or educational system, emphasizing an individual person’s experience of language in its cultural contexts and building up a communicative competence in which languages interrelate and interact, the concept is called ________.
(A) Multilingualism
(B) Lingua franca
(C) Plurilingualism
(D) Immersionism

多語文化(Plurilingualism)：依據多元語言與不同語言

能力之需求，培養終生語言溝通的能力

Plurilingualism is the ability of a person who has competence in more than one language to switch between multiple languages depending on the situation for ease of communication. Plurilinguals practice multiple languages and are able to switch between them when necessary without too much difficulty. Although plurilingualism is derived from multilingualism (also referred to as bilingualism), there is a difference between the two. Multilingualism is connected to situations wherein multiple languages exist side-by-side in a society but are utilized separately. In essence, multilingualism is the coexisting knowledge of separate languages while plurilingualism is the interconnected knowledge of multiple languages.

https://en.wikipedia.org/wiki/Plurilingualism

(B) Lingua franca 通用語