Which of the following is true of HlPCs?
选项：

A:About 100 nations fall in this category.
B:The average debt burden has never been more than 75% of the value of the HlPC's economy.
C:Servicing heavy debt leaves HlPCs with little left to invest in public infrastructure.
D:The annual costs of serving debt consumes about 30% of HlPC export earnings.