下列物质中不需要经过消化就可以由消化道壁直接吸收的物质是（ ）
A：鸡蛋
B：矿泉水
C：面包
D：牛奶
With nothing ________ to burn, the fire became weak and finally died out.
下列关于神经兴奋的叙述，错误的是( )
