哪些因素可增加患Alzheimer病的风险

A．重金属接触史

B．文化程度低

C．母亲怀孕时年龄小

D．脑外伤

E．吸烟

What does the passage mainly discuss

A．( The role of instinct in animal behavior

B．( Observations that suggest consciousness in an anima behavior

C．( The use of food in studies of animal behavior

D．( Differences between the behavior of animals in their natural environments and in laboratory experiment