下列不属于人体免疫器官的是（    ）

关于香港居民的叙述，正确的是（     ）

小宇在同学生日宴会上，敲击注入高度水的几个相同玻璃杯，为同学演奏一曲优美动听的《生日快乐》歌，如图所示注入不同高度的水是为了改变声音的（　　）

　 

    What do you know about the sea? Some people have seen it, but others haven't. The sea looks beautiful on a fine sunny day and it can be very rough when there is a strong wind. What other things do we know about it?

    Of course, the sea is very large. In the world there is more sea than land. If you swim in the sea, you know that the water is salty. Rivers take salt from the land into the sea. Some places of the sea are more salty than other places. Do you know the Dead Sea? Fish can't live in it!