单项选择题

By immersing ore particles in water, ______.

A．we can get ore particles of equal size
B．we can purify aluminum particles
C．we can filter out aluminum
D．we can improve the working conditions around

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单项选择题

In the second paragraph the word paramagnetic means ______.

A．slightly magnetic
B．a weak magnetic field
C．a strong magnetic substance
D．the under-water magnetic power

单项选择题

The best title for this selection is ______.

A．An Ear for Music
B．Music Appreciation
C．How Muscles Participate in Mental Acts
D．A Psychological Definition of the Thinking Process