一个问题China has become the third country______it's astronauts into space after Russia and US.

country 与send 是主动关系 因此用现在分词作country的后置定语能详细简单点吗，要是是被动关系呢，我是个初中生被动用sent 做定语能举举例子吗This is the third letter sent to me. 这是第三份寄给我的信为什么China has become the third country______it's astronauts into space after Russia and US.不能用to send,谢谢，会加分的其实我觉得sending 和 to send 都可以的。只是如果是我举出的那个例子里就要用to be sent 表示被动了。