Online classes began to be popularized just a few decades ago. They are advertised as a way for adults to finish their education and students to learn the material at their own pace—it is far more compatible for people with busy schedules.

        But after being enrolled in an online course last fall semester, I came to realize online classes were merely a means to fulfil course requirements.

         First of all, students lack the desire to learn, and they simply complete their assignments to receive credit for a passing grade rather than genuinely engage with the course material.

        As online courses tend to have more than 100 students, most of the assignments are short and simple. They are not designed for students to interact with the material in depth but designed to be graded easily to accommodate such a large number of students.

         Perhaps the biggest disadvantage of taking an online class is the absence of face-to-face interaction between the teacher and their students. Live sessions are infrequent and are often scheduled during the middle of the day when students have to attend other classes or work. The office hours of the professor may also be during inconvenient times for many students as well. Most interaction with the professor has to be through email which is often impersonal. It is nearly impossible for students to build a relationship with their professor.

        There is also little interaction amongst students. It can be harder for students to create study groups and form relationships with their peers.

        Online classes also require either a computer or laptop and a reliable internet connection. Not all students have access to these types of resources, whether it is for financial or other reasons, and some students can be put at a disadvantage.

        Offering online classes certainly helps students who would otherwise not be able to attend classroom sessions. However, they fail to provide a genuine education with an emphasis on convenience rather than critical thinking. We need restructured online classes in which students can have a learning experience that will actually provide quality education.

解析：D。根据题目中的disadvantage of online classes可定位至原文第五、六段。第五段说到在线课程的最大缺点（the biggest disadvantage of taking an online class）是缺乏师生互动，接着第六段又说到，学生之间的互动也很少。对于学生来说，建立学习小组以及与同龄人建立关系会更加困难。D项与此内容相符，是对第六段最后一句中It can be harder for students to...form relationships with their peers的近义转述，故为正确答案。 

错项排除：A项的at irregular times在原文中无依据，故排除。B项利用原文第五段中的professor和office进行干扰，但原文是说教授的开放办公时间对许多学生来说可能不方便，并不是说教授的办公室不容易进入，B项偷换概念，故排除。第五段倒数第二句提到，与教授的大多数互动都是通过电子邮件，但这并不意味着教授回复学生邮件的负担加重，C项过度引申，故排除。