Due to the advanced technology, online classes provide students with the flexibility of studying in any place with wifi and enable students to connect with teachers far away. The convenience that online classes bring leads to the prediction that online classes would replace the traditional form of study, which is studying in a physical classroom. During the eruption of the pandemic COVID in 2020, schools in many parts of the world temporarily transferred from physical classes as the main way of

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... teaching to online classes as the only way of teaching. Students' feedback towards the efficiency of online classes and physical classes would help improve the educational system. In this study, online questionnaires are distributed to students who both have the experience for physical courses and online lessons experience during COVID in 2020. Feedbacks are collected to compare the efficiency between online learning and offline teaching; factors that influence the efficiency difference are analyzed; suggestions are given for having better studying experience.