A:0.400mol•L﹣1
B:0.300mol•L﹣1
C:0.200mol•L﹣1
D:0.100mol•L﹣1
His order is that all of us ____(get) there before 5 o'clock.
把1999.728四舍五入,使其精确到十位,那么所得近似数的有效数字为( )