一个体细胞的全部DNA"螺旋楼梯"约为A米（）.
A、2
B、3
C、4
D、1
参考答案：A
A．( She was ill
B．( She was afraid
C．( She was anxious
D．( She was excited
机上手提电话的数量为（）个
A.2
B.3
C.4
D.5
