Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.

        A university professor in Singapore gave a two-hour online lecture (26) _______ he didn't realize he was on mute. Professor Wang, who teaches Maths, was not aware that throughout his online presentation, the microphone on his computer was switched off. This meant that (27) _______ of the students attending his online class heard what professor Wang was talking about. His university switched his classes online to help reduce the (28) _______of COVID-19. His lecture started well but then it froze. The video came back but the mic was off and professor Wang did not notice. One of his students says it might have been because the professor was using an iPad and not a computer.

      Students tried many times to contact professor Wang during the lesson but could not get through to him. They waved their arms and even tried calling him on his personal phone. A video of the moment (29) _________he understood his mic was off has gone viral on the Internet. It has received more than 653,000 views. After realizing what happened, professor Wang appeared shocked and stressed. He said he was upset at the thought of wasting two hours of his students' time. He has offered to redo the lecture at a different time so his students do not miss that class. One of his students posted on social media about the professor's (30) _______. She wrote: "I took a class under him before and he teaches well. I feel bad for him.".