相关试题
Newton was playing under an apple tree ____ an apple fell onto his head.
| A．when | B．while |
| C．after | D．before |
I don’t know when he ______. When he ______, I will let you know.
| A．will arrive, will arrive |
| B．arrives, arrives |
| C．will arrive, arrives |
| D．arrives, will arrive |
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