式子$\sigma (a,b,c)$满足$\sigma (a,b,c)=\sigma (b,c,a)=\sigma (c,a,b)$，则称$\sigma (a,b,c)$为轮换对称式．给出如下三个式子：①$\sigma (a,b,c)$=abc；②$\sigma (a,b,c)=a^2-b^2+c^2$；③$\sigma (A,B,C)=\cos C·\cos \left(A-B\right)-{\cos }^{2}C$(A,B,C是$△ABC$的内角）．其中，为轮换对称式的个数是(    )

    Today is Saturday. It's nine o'clock. The Smiths ____ (be) all at home. Mrs. Smith is watching TV. She ____ (like) watching TV and shopping. She wants to buy ____ bike on TV, because she wants to ride it to work. Mr. Smith is ____ (read) a newspaper. There is some news about Liu Huan. And his favorite ____ (sing) is Liu Huan. He sings very ____ (good). Their son, Jim, is talking on the phone. He is calling one of his ____ (friend). He wants to go to the zoo to see animals with his friend. Their daughter, Lily, is playing ____ her small dog. She is only four years old. Look, she's eating a banana. This is ____favorite fruit. What's that over there? Oh, it's a cat. It's sleeping. Jim, please keep quiet ____ don't wake it up!

动物细胞的细胞质的功能是（  ）

下列有关神经调节的叙述不正确的是