He could not get out of the country because he was not allowed. The second sentence, b, tells why he couldn't get out of the country. Someone would not allow him to get out of the country. It could've been for another reason. In this case, it's because he wasn't allowed.Originally Posted by ana2005
Sentence a is a result of sentence b.
If they don't allow him to leave, he can't leave.
They didn't allow him to leave. Therefore, he couldn't leave. [He could've left if they had allowed him to leave.]
Here, "could" refers to past time. However, "could" doesn't always refer to past time. Sometimes it refers to the present and the future.
I would use sentence b to paraphrase the original sentence. The first sentence is really a result of the original sentence. Of course, one might infer that if one is true the other is true within a given context. If you say one, you might be saying the other. It depends on the context and what the listener understands in the first place.
Did your teacher ask you to paraphrase this?