单项选择题

It can be inferred from the passage that______.

A．a stepladder used to have four legs
B．it is dangerous to use tools
C．a tripod is safer in a tool design
D．workers are safer on production lines
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单项选择题
In the past, American families tended to be______.
A．quite small
B．medium sized
C．quite large
D．small
单项选择题
According to the author, the situations of American families in the future may______.
A．become worse
B．remain the same
C．get better
D．keep unchanged
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