Astudy in the 1990s found that residents of mexico city had higher levels of lead and cadmium in their blood than did residents of any other urban area in the world.
what is the most likely explanation for this?
a) diet
b) heredity
c) air pollution
d) water pollution

chronological thinking is an indispensable tool to structure a historical narrative and to give meaning to a sequence of events. the final section presents the results of a survey to test the chronological thinking of lower secondary school students carried out by the educational research institute.