Q:

How to say two things are the most important of something

I am not a native guy and I am having problem with the following sentence.  I would like to know is the following sentence right? 
The A and B are of the most important challenges facing the today world. 

A:

There are many options:

A and B are the two most important challenges ...
A and B are the (key / primary) challenges ...

These statements are all absolute, and mean that there are no other more important "challenges ...".  To soften this a bit:

A and B are (two of / some of / among) the (most important / key / primary) challenges ...

