Reducing unemployment will be the main challenge facing the new government.

=Reducing unemployment will be the main challenge which is facing the government

=Reducing unemployment will be the main challenge which faces the government

参考疑问：减少失业问题是政府面对的主要挑战/难题。

参考疑问：减少失业问题是政府面临的主要挑战/难题。

解答如下：

facing the new government 为现在分词作后置定语修饰前面的名词"challenging"可以改成相应的定语从句。

The immense difficulties facing European businessmen in Russia were only too evident. (现在分词作后置定语修饰前面名词“difficulties”）

在俄罗斯的欧洲商人所面临的巨大困难是显而易见的。