Just use this room for the time being, and we'll offer you a larger one ________ it becomes available.(2010·安徽)

A．as soon as

B．unless

C．as far as

D．until

修改下面的一个病句

我国发明的指南针，不仅促进了世界文明的发展，而且在航海事业中也很有实用价值。