I clean the blackboard for Miss Daisy.

我替戴西小姐擦一下黑板。

Clean the blackboard, please.

请擦黑板。

Need I clean the blackboard now?

我现在需要擦黑板吗？

Please clean the blackboard.

请把黑板擦干净。

We clean the blackboard by turns.

我们轮流擦黑板。