The answer is:
A. Leadership in the Western Empire was weak and emperors and generals fought over land.
C. War, famine, and disease took many lives, leaving fewer people to farm and fight.
When the emperors and generals of Rome fought over land, the military power that Rome owned became separated into smaller units. This make it easier for invaders to conquer various Rome's territories one by one.
When more people went to war, it is very hard for Rome to maintain its agricultural production. This make their Economic income keep decreasing over the years and many of the people sunk into poverty.
