Before plans can be finalized for a space station that maintains a low-earth orbit, scientists must first answer questions about the durability of materials involved in its construction, allowing them to determine which sections of the space station will need the greatest protection and to ensure that such a craft is not overprotected and consequently too heavy.
这个黑体的them指代谁？作者: himba 时间: 2004-8-8 07:56
