A
分析:据小数数位顺序表知:小数点右边第一位是十分位,计数单位是0.1,第二位是百分位,计数单位是0.01,第三位是千分位,计数单位是0.001,第四位是万分位,计数单位是0.0001,0.1>0.01>0.001>0.0001,据此分析判断.
解答:A、0.9801的计数单位是0.0001;
B、0.01的计数单位是0.01;
C、0.1的计数单位是0.1;
D、0.123的计数单位是 0.001;
故选:A.
点评:此题重点考查小数的计数单位,注意0.1>0.01>0.001>0.0001.