单项选择题

Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
What will mainly cause a bug-infected keyboard

A．Eating lunch at desks.
B．Crumbs and food.
C．Poor personal hygiene.
D．Not washing hands after going to the toilet.

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单项选择题

单项选择题

Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. What will mainly cause a bug-infected keyboard 您的浏览器不支持 audio 元素。