4.【2020 •贵州黔南州】While Xiao Ming __________ his homework, his mother came with a cup of tea.
A. has doing B. had done C. is doing D. was doing
【答案】D
【解析】句意：小明在做作业的时候，他妈妈端着一杯茶过来。考查时态。has doing形式错误；had done过去完成时；is doing现在进行时；was doing过去进行时，while当……时候，引导时间状语从句时，从句动作必须是延续性的，后面常跟现在进行时或过去进行时，由came可知本句时态为过去时，所以用was doing，故选D。