问题详情

Wijngaarden will further focus his research on whether
A．there is a definite relationship between high levels of lead and death.
B．the patients with brain tumors have higher levels of lead in their bones.
C．some workers have higher risks of developing brain cancers than others.
D．higher levels of lead have a long-term effect on children over a lifetime.请帮忙给出正确答案和分析，谢谢！