The correct option is B She met with an accident, therefore she couldn't attend college for a month.
A compound sentence is made up of independent clauses that can stand on
their own as sentences. illative compound sentences contain independent
clauses, where one of them is inferred or concluded from the other. "She
couldn't attend... ." is concluded from "She met... .". From the
options, B contains the correct combination, because "therefore" is an illative conjunction that refers to the conclusion. Hence option B is
correct. Option A contains the copulative conjunction "and" which merely
connects two sentences which do not influence each other, hence it is
incorrect here. (The sentences here are related to each other.) Option C
contains the alternative conjunction "or", whereas the required
conjunction must be illative. Hence option C is incorrect. Option D
contains the adversative conjunction, "nevertheless", that expresses
contrast, whereas the sentences do not express contrast. Hence D is
incorrect.