在“家庭状况与学生学业成绩关系”的调查中关于父母的收入的调查是“您父亲的月收入是：A.2000元以下；B．2000至4000元；C．4000至6000元；D．6000元以上”。这种答案形式是（）

A．The number of households surveyed is not very large.
B．The survey was not carried out by the research team.
C．There is no sample from the districts of Ireland.
D．The findings are interesting but not academically useful.