西瓜和葡萄吃起来都有甜甜的汁液,这些汁液存在于细胞的( )
A:液泡中
B:细胞核中
C:细胞质中
D:充满于整个细胞中
若式子σa,b,c满足σa,b,c=σb,c,a=σc,a,b,则称σa,b,c为轮换对称式.给出如下三个式子:①σa,b,c=abc; ②σa,b,c=a2-b2+c2;③σA,B,C=cosC·cosA-B-cos2C(A,B,C是△ABC的内角).其中,为轮换对称式的个数是( )
⑴Can I have an apple, please? ____ A.Thank you.
⑵Do you like milk?____ B.Yes, I like grapes.
⑶Have some pears, please.____ C.OK.
⑷Do you like grapes?____ D.Sure.Here you are.
⑸Let's buy some milk.____ E.No, I don't like milk.
《草原》的作者是老舍。 ( )