单项选择题
A．limb: skin B．foot: toe C．vertebrate: backbone D．insect: exoskeleton E．branch: stem
A．athlete: compete B．salary: tax C．stake: gamble D．production: invent E．role: act
A．visible: sight B．unbreakable: glass C．porous: liquid D．slippery: glue E．reflective: hamper