—_______ did the New Year's Concert last?
—For about 3 hours.
A:How often
B:How soon
C:How much
D:How long
根据氢原子和氟原子的核外电子排布,对F2和HF分子中形成的共价键描述正确的是( )
(Ⅰ)求|AB|;
(Ⅱ)若直线l的斜率为1,求b的值.