血中氨的主要去路是()
A.合成尿素
B.合成氨基酸
C.合成谷氨酰胺
D.合成嘌呤
参考答案:A
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
简述螺旋密封的机理。