The survey found that 25% of babies now have excessive levels of mercury in their blood and hair, and 6% of mothers have mercury levels that exceed the standard. Researchers say that even if the mercury content of fish meets safety standards, if pregnant women are chronically overeating, Consumption will also cause mercury to pass through the placenta to the fetus. Due to the poor excretion ability of the fetus, this mercury will easily accumulate in its body, which will affect the baby's brain development and cause mental retardation. Based on the above text, what is the correct understanding? ['The mercury in pregnant women exceeds the standard, and the mercury in their babies must also exceed the standard.', 'The improper diet of pregnant women is the root cause of retarded infant intellectual development.', "Pregnant women's long-term and excessive consumption of fish can affect infant brain development.", 'The current mercury content safety standards for fish products are unscientific.']