C
题意:当李莉的妈妈____,她正在做作业。
A.在购物 B.在工作
C.正在洗澡 D.在做家务
根据第三段第1-2行:One day, she was doing her homework after supper as usual. Her father was not at home. Her mother was taking a shower in the bathroom.(一天,晚饭后她像往常一样在做作业。她父亲不在家。她妈妈正在浴室里洗澡。)可知,她写作业时,她的妈妈在洗澡。故选C。