What can be inferred from the 2nd and 3rd paragraphs？A．Online course providers have tried

What can be inferred from the 2nd and 3rd paragraphs？

A．Online course providers have tried to ensure the credibility of the exams.

B．The certificates of edX seem to be more credible than those of Open University.

C．Exam halls will gain popularity with the development of online courses.

D．Online courses are seeking ways to make use of traditional testing measures.

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