單項選擇題下列（）對結(jié)構(gòu)類型變量定義是錯誤的。

A.struct teacher {int num; int age; } teach1;
B.struct {int num; int age; } teach1, teach2;
C.struct {int num; int age; } teacher; struct teacher teach1;
D.struct teacher {int num; int age; } ; struct teacher teach1;