Which category is lacking in population age structure diagrams? 

A)  reproductive 
B)  postreproductive 
C)  infant 
D)  prereproductive

Population age structure diagrams typically categorize populations into three main groups based on potential for reproduction: prereproductive (young individuals who have not yet reached reproductive age), reproductive (individuals in their reproductive years), and postreproductive (individuals past their reproductive years). The category "infant" is not specifically delineated in these diagrams, as infants are included within the broader prereproductive category.