“甲型H1N1流感病毒”的H和N分别指的是病毒表面的两大类蛋白质——血细胞凝集素和神经氨酸酶，病毒结构如图所示。下列叙述正确的是

在正方形ABCD中，点E，F分别在边BC，CD上，且∠EAF=∠CEF=45°．

    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!