Can someone please help me??

What's the waste product of electrons and pyruvate combining in fermentation?  

To take a whiff of your favorite food, you use both? a. motor nerves and your digestive system b. sensory nerves and your immune system c. motor nerves and your skeletal system d. sensory nerves and your respiratory system

Na convection cycle, what causes plastic-like material to sink a. it loses heat to the crust. b. it gains heat from the crust. c. it loses heat to the outer core. d. it gains heat from the outer core.