Modifier

"known in English as Doctors without Borders" is describing "Medecins sans Frontieres" and not "Doris Schopper" .. The reason is that "known.. " is right next to "Medecins sans Frontieres"... Also, if we see the meaning of the sentence then it's clear that author is elaborating the meaning of non-english part.

appositives sit next to nouns and identify or define them. In the sentence that you have posted - medicine sans frontier is Defined as doctors without frontier. Therefore doctors without frontier must sit next to medicine sans frontier. this was option A does.

Here is one more example of an appositive used as a modifier.

1. Next, the reporters questioned Juliana.

2. Juliana is the candidates wife.

If I combine these two sentences I can write

Next , the reporters questioned Juliana,the candidates wife.

Look how. - the candidates wife sits next to Juliana and describes her.