Online distance learning is an instructional system which connec

Online distance learning is an instructional system which connects learners with educational resources．Students work on their own at home,at work,or at school and communicate with faculty and other students by means of e-mail,electronic meetings,videoconferencing,chat rooms,instant messaging and other forms of computer-based communication．There are both advantages and disadvantages to online distance learning. There are many benefits to using online distance learning environments．Online education is available all the time,anywhere and to all people．However,there are weaknesses for some learners．The online learner only has the written text and no other face-to-face hints．This may confuse the learner and cause misunderstanding．While distance learning allows for an openness,it is also difficult because it is done by e-mail messages and writing,and therefore may take more time than face-to-face learning．Sometimes the messages can be overwhelming for many online students. Universities,colleges and schools use online distance learning environments．These are important for students who may be unable to attend classes for various reasons like illnesses or busy everyday schedules．Some learners just want to further their studies at home．They enjoy the convenience of home learning as they take regular programs or enrichment classes. Online courses keep learners very occupied at all hours of the day．There are a great many messages and other online resources to read and respond to．Most learners have regular jobs or attend regular school classes on ground as well．However,the benefits are clear．Online distance learning is becoming very popular．Some online classes have become a profitable business as they replace regular traditional means of learning. Sometimes online distance learning can be a problem because__.
A、learners can't afford it
B、learners get too many hints
C、it involves excessive writing
D、it is not available at the weekend
【正确答案】：C
【题目解析】：根据给出的文本，我们可以逐项分析选项： A. learners can't afford it（学习者负担不起）：文中没有提到在线远程学习的高昂费用是学习者面临的问题，因此A选项不正确。 B. learners get too many hints（学习者得到太多的提示）：文中提到在线学习者只有书面文本作为学习材料，并没有提到他们得到“太多的提示”，因此B选项不正确。 C. it involves excessive writing（它涉及过多的写作）：文中明确提到“it is also difficult because it is done by e-mail messages and writing, and therefore may take more time than face-to-face learning. Sometimes the messages can be overwhelming for many online students.” 这意味着在线学习由于涉及到电子邮件和写作，可能会比面对面学习更耗时，对于许多在线学生来说，这些消息可能是压倒性的。因此，C选项正确。 D. it is not available at the weekend（它在周末不可用）：文中没有提到在线学习在周末不可用，反而提到“Online education is available all the time, anywhere and to all people.”，因此D选项不正确。 综上所述，正确答案是C，即在线远程学习可能成为一个问题，因为它涉及过多的写作。