— The _____ of July is your birthday. What do you usually do?— I usually help my mother with some ho

题干

— The _____ of July is your birthday. What do you usually do?

— I usually help my mother with some housework because I want her to have a rest _____ that day.

A：first; on

B：one; on

C：first; in

D：one; in

上一题下一题 0.0难度选择题更新时间:2018-08-08 06:01:23

A

某港口的水深y（米）是时间t（0≤t≤24，单位：小时）的函数，下面是每天时间与水深的关系表：

t	0	3	6	9	12	15	18	21	24
y	10	13	9.9	7	10	13	10.1	7	10

经过长期观测，y=f（t）可近似的看成是函数y=Asinωt+b

（1）根据以上数据，求出y=f（t）的解析式；

（2）若船舶航行时，水深至少要11.5米才是安全的，那么船舶在一天中的哪几段时间可以安全的进出该港？