You want it, we have it, _____ a very good price. [ ]
A. for
B. at
C. of
D. in
答案:B
关系模式A的码是( )。
A.C
B.(H,
C.(H,
D.(H,
下列是由胰腺内分泌细胞所分泌的物质有( )。
A.胰岛素 B.碳酸氢盐C.淀粉酶 D.核糖核酸酶