A:Where does your mother work?
B:What's her job ?
C:What does he do ?
某小区居民王先生改进用水设施,在5年内帮助他居住小区的居民累计节水39400吨,将39400用科学记数法表示(结果保留2个有效数字)应为( )
____ ÷16 =____:24=0.75=3÷____=____%=____折.