One important advantage of online courses is that they offer ______________ classes. People can decide when to learn.Đoạn văn10/45Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions. One important advantage of online courses is that they offer ______________ classes. People can decide when to learn. high-qualityflexiblesuitablecheapGiải thíchChọn B