In this section, you will hear several news items.
Listen to them carefully and then answer the questions that
follow. Questions 21 to 23 are based
on the following news. At the end of the news item, you will be given 15 seconds
to answer the questions. Now, listen to the
news. At the present time the brush can NOT be used to ______.
A．sweep up tiny pieces of nanodust B．paint microstructures C．soak toxins from water D．find medical uses