The relative pronoun is ''Which'' because relative pronouns connect to a clause or phrase to a noun or pronoun.
1. Archaeologists - study of cities, artifacts, and customs of the ancient world.
2. Linguistics - dealing with language or the study of languages.
3. Tounges - the languages of people or nationalities.
4. Idiom - a phrase or expression whose meaning cannot be taking literally.
If you need explaining let me know. Hope this helped :)
The third sentence:
Ming and her sister, who is home from college for spring break, organized a bake sale to benefit the victims of the fire.