Question

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1. his parents work at a plant.( Where. Who)
2. My sister studies English at school.(what language)
3. he cleaned the blackboard after lesson.(when. who)
4. he went to work in the afternoon.(Where. disjunctive)
5. she will come back at 3 o clock. (when. alternative)

Answer 1

1 who works at a plant? Where do his parents work?
2 What language does my sister study?
3 Who cleaned the blackboard after lesson? When did he clean the blackboard?
4 Where did  he go to work? He went to work in the afternoon(не правильно, посмотрите) didn*t he?
5 When will she come back ? Will she come  back at 3 or at 5 o*clock ?