题文
There are still many problems ______ before we are ready for a long stay on the Moon.
| A．solving |
| B．solved |
| C．being solved |
| D．to be solved |
推荐试卷
There are still many problems ______ before we are ready for a long stay on the Moon.
| A．solving |
| B．solved |
| C．being solved |
| D．to be solved |
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