Answer:
which do you believe is the most serious in terms of foreign affairs
The rise of China is one of the most serious challenges that the U.S. faces. China is growing economically at a faster pace, it has a larger population, it has the largest standing army in the world (even if the U.S. army is more powerful, this is something to take into account), and its influence in some areas like Eastern Africa and Central Asia is growing.
which do you believe is the most serious in terms of domestic affairs
Growing economic inequality presents a challenge. Very unequal societies like those of Latin America tend to be very conflictive. The U.S. could face similar consequences in terms of security and social cohesion if economic inequality continues to grow.