下图是某生物的精细胞,根据图中的染色体类型和数目,产生这五个精细胞至少需要精原细胞和次级精母细胞的数目依次是
A.2、2
B.2、3
C.3、4
D.2、4
答案:D
— Is her sister a teacher or a student?
— _____________.[ ]
A. No, she's a teacher.
B. No, she isn't a teacher.
C. She's a student.
D. Yes, she's a teacher.
电荷的流动一般称为电压。